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Fishery Products

( Originally Published 1939 )


When it is recalled that water covers about three-quarters of the surface of the earth, and that it abounds in animal (and vegetable) life throughout both its area and its depth, some idea of its enormous potentialities for human food may be realized. However, only a relatively small part of its animal life is utilized in this way. Such neglect is largely due to lack of knowledge as to food value and edibility of many species, as well as to absence of technology adequate for their procurement and preparation as food. As information is slowly acquired, new varieties of sea life are being utilized. Several of our largest sea-food industries have grown up within the memory of men now living. Some fish are avoided because they have been thought to be poisonous; some are neglected because knowledge of their proper handling is not available; and others are not used because of prejudice, as for example, dogfish (by reason of its unfortunate name) . Research in natural history, culture, and technology of marine food products is slowly pushing back this great frontier.

Fish. Most of the annual catch of fish is taken with seines, lines, traps of various sorts, and different kinds of nets.' Properly iced fish should keep fresh for several hours, but when kept longer they become stale and deteriorate rapidly. Ice-packing retards these changes somewhat, but even when heavily iced and properly handled, fish cannot be kept in acceptably edible condition for more than 2 or 3 weeks. Some operators incorporate mild antiseptics (harmless to human beings) in the ice to retard microbic development. These chemicals, such as boric acid, drain off in the ice water, and do not remain on the fish.

The catch is sometimes eviscerated at sea, washed with sprays of water, and packed in holds of fishing boats in ice. At the packing plants, they are hoisted out in large canvas baskets and dumped into wash tanks of running sea water. Scales are removed by machines. The fish are again washed, fillets are trimmed out by hand, skin is removed (sometimes by machinery), and dressed fillets are inspected on tables, wrapped, packaged, and frozen in the final container. Some-times fillets are molded into steaks and packed into manila-board, paraffin-coated cartons which are wrapped with moisture-proof Cellophane.

Freezing. In general, the colder the temperature, the slower are the deteriorative changes. This has led to the freezing of fish at temperatures as low as -25° F. (—32° C.). Of the several industrial methods of freezing, the use of cold air alone is the slowest and possibly the oldest.' Improvements in freezing technology led to immersion of fish in cold brine, or to removal of heat by conduction through metal plates which are in contact with refrigerated brine. Sometimes fish are frozen by placing the packages between refrigerated traveling belts or between the refrigerated plates of a vertical press. Even so, the rate of heat removal is so slow that "quick-frozen" pieces cannot be more than 3 inches thick.

When fish are frozen rapidly, the gelatinous contents of the muscle cells solidify as a mass of frozen jelly, whereas, if freezing takes place slowly, there is a tendency for the water content to separate from the jellylike mass and to rupture the delicate cell walls. When the fish are defrosted, these juices or extractives drain away. The temperature range of maximum damage is 32° to 23° F., and is roughly proportional to the time of exposure.

In order to protect the frozen fish from oxidation, dehydration, and other deterioration from exposure to the air, the frozen fish are often coated with a thin glaze of ice. Some fish before freezing are packaged and wrapped in moisture-proof Cellophane. Deterioration occurs rapidly after frozen fish are thawed. Some authorities recommend that fish be cooked directly without thawing.

When fish are taken from the water, they become covered with a slime which harbors great numbers of microorganisms. This contaminates all the fish-handling equipment, and necessitates properly constructed plants and effective sanitary methods of operation. Chlorinated sea water must be lavishly used throughout the plant to keep it clean.' The brine solution in which the fillets are immersed to reduce the "drip" (see page 455) is kept chlorinated. All the surfaces in the plant must be smooth finished, non-porous, and easily cleaned. The floors should be concrete, sloped to frequent drains. The walls and ceilings should be enameled white. Metal parts should be non-corrosive; they are usually of Monel metal or stainless steel. Rubber gloves for the hand operations have not proved satisfactory because pieces of fish adhere to them, but the operators rinse their hands in chlorine water. The whole plant must be kept flushed clean during the day and scrubbed down every night.

Salting. In the preservation of fish by salting, there is an osmotic passage of water outward from the fish tissues, and a penetration of the salt into them. This combined dehydration and increased salt concentration in the tissue fluids inactivates the enzymes and holds bacterial growth in abeyance. A salt solution of 4 percent strength retards decomposition, and one of 20 percent strength practically stops it. The most general method in commercial salting is to rub the washed and dressed fish with 10 to 35 percent by weight of dry salt, and then to pack them in water-tight containers in alternate layers of fish and salt. Tressler has shown that the presence of calcium and magnesium retards the penetration of the salt into the fish and effects less preservation as shown by the increased amounts of amino acid nitrogen that are produced during storage. After several hours, the osmotic effect of the salt has drawn enough water from the fish to form a pickle to cover them. They are then allowed to stand undisturbed until packed in fresh pickle or dried. Some of the smaller fish are salted without evisceration in order to impart certain desired flavors, but the larger fish are carefully eviscerated, bled, and washed. The more completely this cleaning is done, the better the fish will resist bacterial and autolytic decomposition, as Tressler has shown. But salting does not prevent the oxidation and development of rancidity of the fish oils. The more fatty fish, such as herring, alewives, and mackerel, undergo this type of deterioration to a much greater ex-tent than cod, haddock, and other lean fish. This type of spoilage manifests itself as a darkening or "rusting" of the fish, together with the development of rancid flavors and odors. Storage under brine in cool warehouses retards these changes.

Smoking. In the preservation of fish by smoking, the general treatment is to give them a preliminary salting, followed by the smoking treatment. The first effects a slight drying as well as a passage of salt into the tissue, and the smoking removes more water and deposits the constituents of the smoke in the tissue. These products of combustion consist of various preservatives in wood creosote, dependent on the kind of wood and the conditions under which it is burned. Small fish are usually smoked without evisceration, whereas large fish are carefully gutted and split. In the cold smoke process, the temperature does not exceed 80° F. (27° C.), and may last from several hours for the lightly processed kippered products to several weeks. In the hot smoke process, the treatment is completed in several hours and cooks the fish.

Canning. Fish is canned on a very large scale, particularly salmon, sardine, shad, tuna, herring, mackerel, cod, and haddock. The head, viscera, blood, and tail fin are removed. The fish is washed, and then is trimmed to pack into the cans. Most of this is done by hand, but machinery has been developed to can sardines and salmon mechanically. To secure a desirable body and flavor, many kinds of fish are held in brine before they are canned. Some are cooked, and others like sardines are dried before canning. They are then placed in the cans, heated in a steam chamber (or "exhaust box") for a short time, and hermetically sealed. Sometimes the insides of the cans are coated with an enamel lacquer, especially if the fish products contain sulphides. The tops are sealed onto the can bodies by crimping and then rolling (or double seaming) them together, over a gasket of cement, rubber, or paper to insure their hermetic closing. Fish packs quite solidly so that the rate of heat penetration is slow. To in-sure sterilization, the cans are processed in steam pressure retorts at temperatures of 230° to 240° F. (110° to to 116° C.) for various times according to the contents and the size of the can.

Drying. When fish are to be preserved by drying, they are first cooked to sterilize and partially dehydrate the tissue. Dried fish do not reabsorb water back to the moisture content of the fresh fish. Long storage makes them tough and rubberlike by reason of the denaturation of the proteins and the oxidation of the fat.

Oysters. Production. These shellfish are grown to the best ad-vantage in brackish water, containing from 1 to 3 percent salt, preferably nearer about 2 percent, at depths from the low-tide mark down to 30 feet or more. Their food is microscopic plants, chiefly diatoms and other organic matter suspended in the overlying waters. Inasmuch as the food must be brought to them, they thrive best in waters with strong tides or currents. The very great demand for this bivalve has resulted in such a depletion of the natural beds by over-fishing that oyster culture is being practiced extensively. Desirable bottoms are leased by states to growers, who develop oysters in their natural beds, or plant and grow new ones. Success in this oyster farming, as it is sometimes called, largely depends on the freedom of the oyster beds from starfish and other marine enemies, an adequate food supply, other natural requirements for good oyster growth, and the ability of the police to protect the enterprise from free-lance oyster poachers. A crop is usually ready for marketing in 3 to 5 years.

In shallow waters, oysters are often harvested from small flat boats by tonging. The tongs are poles, from 12 to 20 feet long, fastened together like scissors, and equipped with toothed iron baskets at the ends. The oysterman stands at the side of his boat, lowers the baskets to the oyster bottom, and scoops up the oysters. They are harvested at greater depths by power dredges. Oyster boats deliver the stock, with more or less adhering mud, to shucking houses on land.

Packing. Shells are opened by prying into them with a sharp strong knife, then thrusting the knife farther in and cutting the strong adductor muscle, thereby allowing the shucker to raise the top shell, cut the meat free from the lower shell, and slide it into the bucket. Sometimes a small amount of water is placed in the bottom of the bucket. Shucked oysters are washed free from mud, bits of shell, and mucous in large tanks of slightly saline water, agitated by "blowing" air into the water at the bottom. This treatment keeps the oysters in motion without tearing the delicate meats. Extraneous material settles to the false bottom. If prolonged for more than about 3 minutes, this practice results in the oysters absorbing excessive amounts of water. The oysters are strained out of the tanks, packed in cans with tightly fitting covers, and kept well iced. Shucked oysters generally run higher in bacteria counts than they did in the shell owing to the pickup of bacterial contamination in handling and in contact with plant equipment, and especially to multiplication.

Canning. In packing oysters for hermetic sealing in cans and sterilization by heat, the stock is placed in iron cars and run into horizontal steaming chests. Doors at the ends are closed, and steam under several pounds pressure is turned into the box. This treatment kills the oyster and allows the shell to open. The oyster liquor drains out and is lost. Shuckers quickly cut the more or less shriveled meats from the shell, and weigh them into 3- to 10-ounce cans which are filled up with brine. Oyster meats will absorb a small amount of water from this brine when they have stood in it for several hours so that the cut-out weight, as it is called, of canned meats is always more than the weight of meats when packed. The packer allows for this increase in final weight by setting his scales to weigh a proportionately smaller amount into the cans so that the drained weight of the final pack will equal the claimed weight. The cans are hermetically sealed, and sterilized in autoclaves under steam pressure at 240° F. (116° C.). Sometimes canned oysters are called cove oysters, probably from the early practice of collecting such stock in small coves along the rivers.

Self-purification. Oysters from slightly polluted waters can be made wholesome by transplanting them to clean waters where they clean themselves by discharging harmful microorganisms. This process of self-purification has been improved by storing oysters in water containing hypochlorites. Oysters are dumped into shallow tanks or basins, covered with water of approximately the same salinity as that of the original beds, and treated with calcium hypochlorite or liquid chlorine to give a chlorine content of several parts per million. Chlorine sterilizes the water so that oysters can cleanse themselves effectively. They do not open their shells and feed if the water contains excessive amounts of chlorine. Discharged intestinal contents, together with other organic matter, use up this original chlorine so that a second dosage is necessary. After oysters have lain undisturbed in this chlorinated water for a total period of about 24 hours, they are ready for shipment. This treatment not only greatly reduces bacterial content but also loosens dirt from the shells and therefore lessens contamination during shucking. Carmelia states that scores are reduced 90 percent, but he recommends that no oysters with scores above 230 to 320 be treated by this method, in order to allow a reasonable margin of safety. In England and at the State Shellfish Demonstration Plant at Willoughby, Norfolk, Va., the shellfish are held in sea water which had been previously chlorinated to free it of fecal organisms but containing no chlorine during the holding treatment.

Floating. In commercial practice, it is necessary to carry a stock of shellfish from which to fill unexpected orders, and to provide a reserve for those periods when weather conditions make it impossible to obtain oysters from offshore beds on account of storms or ice. Shellfish shipped directly from water will remain fresh longer and reach market in better condition than oysters that are shipped from dry storage bins. Also, shells of oysters for serving on the half-shell should be as clean as practicable. All these desiderata are secured if the oysters are stored under water. This practice is called floating. If the overlying water contains less salt than the original water in which the oysters were grown, some water dialyzes into the oyster meat. This action increases the size of the oyster, which is then said to be "fattened" or "plumped." Some unscrupulous dealers have taken fraudulent advantage of this treatment to impart a deceptive appearance of fatness. Such adulteration with water is not practiced now because this deception can be achieved more easily and cheaply by simply adding water to shucked stock. Floating consists in placing market stock in artificial floats, on bottoms in inshore waters, or in tanks ashore. Under these conditions, waters are often polluted, and stock from clean areas may become contaminated in handling and storage. Several states have enacted legislation to restrict or prohibit this practice. Floated stock from polluted waters is prohibited in interstate trade.

Cleansing plants. Several cleansing plants have been erected for controlled self-purification of oysters,' clams, and mussels."

Clams. Although a number of species of clams are fished, the great bulk consists of soft clams, produced mostly north of New York; hard clams or quahaugs (also called cherry-stones or little necks in the smaller sizes), produced from Cape Cod to Texas; and razor clams, produced on the Pacific Coast from Oregon to Alaska.'

Soft clams are usually dug from shallow waters near shore or on dry flats from which the tide has receded. The clam digger digs with a clam hoe or fork in mud or sand to a depth of 6 to 10 inches, and collects the upturned clams. Small clams, suitable for steaming, are usually shipped to market in the shell, but unsightly mud clams are shucked. Meats absorb considerable quantities 6f water, and Tressler states that in 6 hours they increase in volume about one-third. Shell stock is ordinarily shipped in second-hand barrels, and meats in kegs or tubs.

Hard clams are sometimes dug out of flats by means of short rakes, but the bulk of production is obtained from deep water by raking the bottoms with long-handled rakes, 25 to 65 feet long, or with tongs similar to those used for oysters. These are operated from boats anchored over the beds. The rake is lowered from the bow of the boat, the teeth worked into the bottom, and the rake worked back to the stern of the boat where it is hauled in. Dredging is sometimes practiced, with a deep-water clam dredge. Clams are washed on shore, graded into the several commercially recognized sizes, and shipped in well-ventilated barrels or bags. Inasmuch as quahaugs are hardy and live out of water a long time, they can be shipped to inland points in good condition.

Razor clams, produced on the Pacific Coast, are fished by digging into sand between tide lines with short-handle spades. This species constitutes the great bulk of the canned-clam industry. Some plants have automatic shucking machinery which removes the meats by passing the clams through hot water to cause the clams to gape, and then by shaking the meats out of the shells. The meats are dressed and cleaned, then minced in a meat grinder, and packed into cans from automatic filling machines. The natural juice is added, and the cans are exhausted to produce a reduced pressure when sealed, hermetically closed, and processed at 220° F. (104.5° C.) for 90 minutes, for 1-pound cans.

Like oysters, clams are subject to contamination from polluted waters. The soft clam and the razor clam are particularly susceptible because they are mostly fished from beds between the tide lines which are relatively close inshore. The city of Newburyport has built and operated a plant for chlorine treatment of clams. It is licensed by the Commissioner of Health and must operate according to official rules and regulations. Among other provisions, these require that shellfish must first be washed in sterile seawater or other approved water, that this water must contain 0.5 p.p.m. of available chlorine 15 minutes after application, that stock. must be subjected to chlorine treatment for at least 24 hours, and that all records of sources and treatment shall be kept for official inspection. The operation is re-ported to be practicable. Large clam-growing areas have been re-claimed, and work has been provided for hundreds of men. Such a plant for the chlorination of shellfish has been authorized for treatment of clams for New York city consumption.

Scallops. The scallop is a species of mollusk. The small or bay type is obtained in commercial quantities along the Atlantic seaboard from Massachusetts south to the Gulf. The giant or deep-water scallop is fished mostly off the coast of Maine, but also in scattered areas as far south as the Carolinas. These shellfish are free-swimming, and are caught by dragging special bagnets or dredges over the bottoms. Although the whole scallop is reported to be edible, the only part that is marketed for human consumption is the adductor muscle or "eye" as it is called. Sometimes these meats are soaked in water to plump them and increase their size, but this practice is illegal.

Mussels. Mussels grow extensively on northern Atlantic and Pacific coasts in the slightly brackish shallow waters of protected bays in swift tideways. Their growth under these conditions often renders them liable to pollution. They attach themselves to fixed objects and often form very extensive beds. They are harvested by rakes and dredges. Mussels spoil quickly after removal from water, and shucked meats likewise deteriorate rapidly. This prevents the long-distance shipment. The most common method of preservation is pickling. They can be canned without undergoing shriveling like oysters, and they have an attractive appearance and pleasing taste. At Conway and Lytham in England, mussel self-purification is practiced somewhat similarly to purification of oysters and clams in this country." Mussels are given a succession of baths in sterile water. They purify themselves by discharging their own content of bacteria and other pollution, and then a final bath in chlorinated water sterilizes the outside of the shell.

Shrimp. This crustacean is fished from North Carolina to Texas, the largest production being in Louisiana. The peak of the catch, in October, consists mostly of young immature shrimp derived from the spawning of the preceding spring and summer. As cold weather approaches, large shrimp move into deeper and warmer waters of the outside, and only small ones remain in sounds, bays, and bayous. Formerly, the haul seine was used, but it has been almost completely replaced by the otter trawl net. This consists essentially of a bag-net of 11/2 to 2-inch mesh, 22 to 100 feet in width, provided with wings on each side to direct the shrimp into the bag, and with otter boards on the extreme ends of the wings to hold them apart and direct the course of the net downward so that it drags constantly on the bottom. Power boats drag the nets slowly for about 2 hours between hauls. When fishing is conducted at a considerable distance from the packing houses, ice boats visit the fishing fleet to bring the catch to shore sooner than they would be brought by the slower and less well equipped fishing boats. Boats are out usually about 3 days.

Inasmuch as the supply comes from waters where warm weather prevails, the industry has suffered large losses by the official seizure of large quantities of decomposed stock. Inadequate icing of boats, unclean holds, insanitary packing-house practices, inadequate equipment, and uncontrolled processing all have contributed to spoilage. Detection of decomposition of raw shrimp is comparatively simple but is possible in the canned product only when spoilage had progressed to a pronounced degree before canning: Chemical tests have proved in-adequate to determine whether the canned product was packed from raw decomposed stock, but certain odors of such products are characteristic and definitely identify them. By this means, regulatory officials have condemned such large quantities of unsound canned shrimp that a demand arose for an inspection ,service to correct the trouble at the source and insure the packing of a sound product. In 1934 Congress enacted the "Seafood Amendment to the Federal Food and Drugs Act," and a large part of the shrimp industry is operating under this voluntary inspection system.

When the head (and closely associated stomach) is removed within 30 minutes of the death of the shrimp, the objectionable "black streak" or intestinal tract is taken out in the same operation. If there is greater delay, it does not come out with the head. Heads, stomachs, and shells are removed by hand. Meats are washed and blanched in hot brine in cypress tanks. Before blanching, meats are white, but this treatment turns them red. They are cooled on trays, picked for refuse, and graded. In the wet pack, meats are filled into cans, and covered with a 2.5 percent hot brine. In the dry pack, cans are lined with paper to reduce the formation of black sulphide from the iron of the can. No. 1 tins are given a heat process of 240° F. (116° C.) for 60-75 minutes for the dry pack, and 10-12 minutes for the wet pack. Sometimes crystals have been found in canned shrimp, believed by consumers to be glass. This is harmless magnesium ammonium phosphate, formed after sterilization of the can, and is readily dissolved in the stomach. An odor resembling that of iodoform is occasionally noticed. This is caused by marine organisms which were eaten by the shrimp.

Fresh headless shrimp are marketed by packing 125 pounds in a barrel, between layers of ice, or packed around a large central cake. Sun-dried shrimp, produced from sizes too small for canning, are ex-posed to the sun on specially designed wooden platforms where they dry in the summer in 3 to 4 days or in the winter in 5 to 10 days. Heads and shells are removed by special machines which separate meats mechanically. These are packed in barrels of 210 pounds. A large amount of quick-frozen shrimp, some headless and peeled and some not headed, is now being marketed. A small amount is sold directly as freshly cooked meats, and some in a pickle brine.

Crabs. Three species of crabs in United States waters have been developed to support a large and distinct industry, namely, the blue crab (and to a less extent the sand crab) of the middle and southern Atlantic Coast and the Gulf of Mexico, the rock crab of New England, and the edible crab of the Pacific Coast.

Hard-shell crabs are caught with trot-lines, dredges, and scrapes. The trot-line is a line several hundred feet long to which bait is attached at short intervals. It lies on the bottom and is raised as the crabber moves his boat along its length. Crabs are caught in dip nets as they are brought to the surface. In winter, crabs are captured on the bottoms by means of dredges. Although some hard-shell crabs are shipped alive in well-iced barrels, the bulk is steamed. Steamed crabs may be served whole to the consumer, who breaks open the shell and claws, and picks out meat as he eats it. Increasing quantities of steamed crabs are now handled in packing houses where meats are picked out by employees and shipped as crabmeat. The shells from this operation are cleaned and sold for serving deviled crabs. [See also Nickerson, Fitzgerald, and Messer. Am. J. Pub. Health, 29 619 (1939)].

Soft-shell crabs are molting young crabs caught in warm months of late spring, summer, and early fall, mostly in June and July. The bulk of the supply is obtained by placing crabs which show signs of shedding their shells in shallow floats, although some are scooped directly from the water with small dip nets or scrapes. Scrapes are triangular iron frames which hold open mouths of cotton-mesh bags for dragging along the bottom. Soft-shell crabs are very tender and perishable. They are shipped alive in trays in crates, packed between layers of seaweed, well iced and covered with parchment paper.

Crabs are canned on the Pacific Coast and Alaska by packing the meat in cans lined with parchment or oiled paper and processing under steam pressure. Most of the canned crab meat is imported from Japan and Russia.

Discoloration or blackening of canned crab meat has been found to be due to the formation of iron sulphide, after the crab is canned. As the meat becomes alkaline, the sulphide develops, and this reacts with the iron of the can. Double-lacquered cans have been reported as preventing this trouble. Also a buffer solution, preferably tartrates or citrates, prevents it. There is reported to be no blackening below a pH value of 7.0.

Blue crabs, whose freshly picked meat is marketed so extensively in iced tins, have not been successfully canned by heat sterilization except by one company which has a secret process. Unattractive shades of blue or gray, sometimes almost black, may develop within a few days or weeks after canning. This is caused by a color reaction between copper and ammonia, both liberated from the crab tissue by heat. Fellers 14 has found that such discoloration can be prevented by heating crabmeat with an aqueous solution of salts of aluminum, zinc, or tin, in concentration of 50-500 p.p.m. The strength of the solution depends on the salt used and the duration of the treatment. As an example, the meat may be merely dipped in a solution of 400 p.p.m. and then thoroughly drained and washed before packing into the cans and sealing. Sterilization should also be at a low temperature —not above 240° F. (116° C.).

Crabmeat. Production of fresh cooked crabmeat is increasing. It is now produced in ten states on the Atlantic and Gulf coasts, in the Pacific Coast states, and in Alaska. In this category also are lobster meat, shrimp, and crayfish.

In preparing this food for market, the crustaceans are cooked in large retorts or open kettles. The contents are dumped on work tables, cooled, and trimmed. The shells are broken open and the meats picked out by hand. Grading is based on the part of the body from which the meat is taken and on the size of the pieces, or flakes as they are called. Meat from the body of the crab is white, and that from the claws brownish white. The meat is washed, weighed into cans, and packed in ice for shipment. This product is extensively used for cocktails, salads, and certain cooked dishes.

The conditions which have generally obtained heretofore in this industry have constituted serious sanitary problems. Many plants have been located in insanitary surroundings and operated under conditions which exposed the meats to serious contamination. Drainage was often poor so that operations were subject to hazards of flies and sewage. Workers were usually recruited from the class who were ignorant of, and more or less indifferent to, demands of sanitation. Presence of Escherichia coli demonstrated that products were contaminated with fecal matter and were a health hazard. Recognition of these deplorable conditions has led to a drastic cleanup of the industry. Food-control officials made many seizures, and courts have supported their efforts with effective fines. A traveling control laboratory has been provided for visiting plants on extreme southern coasts. Various states where crustacean meats are packed have issued regulations and are vigorously enforcing them. As a result of all this regulatory effort, supported by the better elements in the industry itself, conditions have so markedly improved that the products now sold are reasonably clean and safe.

This improvement has been brought about by means of proper equipment and the application of sanitary and efficient methods. It is necessary that the buildings be well lighted, proofed against access of vermin, and constructed to be cleanable and sanitary. All small equipment coming in direct contact with meats, such as pans and knives, are cleaned and sterilized frequently. Operations must be supervised to prevent setting pans of crabmeat on top of one another. Operators are required to wash their hands with soap, and dry them on clean towels before beginning work. Ample sanitary toilet pro-visions are necessary. All these control measures are generally recognized as simple hygienic practices. Their conscientious and intelligent application is enabling operators to put out clean and safe products.

Sometimes crabmeat has been found to contain small solid partiéles which consumers have thought were powdered glass. These have been shown to be crystals of magnesium ammonium phosphate which naturally are present in the flesh of some crustaceans and are harmless when ingested. Also, canned crustaceans are often rejected because of the accumulation of a white deposit of tyrosine which is mistaken for mold.

In general, fish contains more water, less fat, and a little less protein than typical meats. On a fat-free basis, fish runs about 10 per-cent lower in percentage content of protein than typical meats. Its ash tends to run higher than that of meats. Fish is a poor source of carbohydrates, and some varieties run low in fat. Oysters are next to liver in percentage content of copper. Shellfish are not rich sources of either fat or carbohydrate, although they do contain 12 percent of glycogen, sometimes called animal starch. Oysters, mostly from the vicinity of New York and New England, have been reported to contain arsenic as As203 to the extent of 0.6 to 3.5 milligrams per kilogram, copper 4 to 2118, zinc 394 to 3107, and lead in traces."

A certain amount of free natural liquor in shucked oysters gives occasion to adulterate them by the fraudulent addition of water. In the commercial operations of shucking, blowing or washing, and skimming, wash water may be added. As the result of many experiments and numerous tests to ascertain how to determine when oysters are adulterated with water, the U. S. Department of Agriculture has found that the amount of liquor that drains off of normal oysters averages about 5 percent when measured by official methods. The data in Table XXIX are taken from figures on shipments of normal oysters and those to which known amounts of hydrant and wash water were added, to ascertain how much free liquor develops during shipment, and the extent to which oysters, if adulterated with fresh water through deliberate intent or improper draining, will absorb this excess of liquid.

These data show that, unless the source of the stock is known so as to identify the chemical composition with the type of oyster, chemical data are not nearly so useful as the determination of free liquor. Oysters of high solids content absorb and hold more water than thinner stock. Additions of 10 percent water can usually be detected.

An excess of 10 percent of free liquor by volume indicates that oysters are adulterated. Added water dilutes the solids, salt, and moisture, but inasmuch as these constituents vary with locality, the most reliable test is determination of free liquor.

When oysters are floated or washed in water which contains less salt than that in which they were grown, some salt is extracted from them and water dialyzes into the meats. The result is a less tasty, softer, paler, plumper, or "fatter" oyster. The volume may increase as much as 30 to 40 percent. As when water is directly added, such floated or fattened oysters will drain a greater amount of water than the normal 5 percent. The U. S. Department of Agriculture will prosecute any adulteration of either shell or shucked stock with water by the floating treatment 18 or other means.

Nutritional value. Several investigators have shown that lean fish and oysters are about as digestible as lean beef, and that fat fish, crabs, and lobsters are similar in digestibility to fat meat. The fat itself is about as digestible as any animal fat. Similarity in quality of shrimp muscle and halibut flesh to other meat is shown by figures in Table XXX compiled from Jones, Sherman, and Tressler. Her-ring and haddock proteins are reported by Kik and McCollum to be poor supplements for proteins of navy beans and peas, but they do have a supplementary value for proteins of oats and wheat. They are not fully the equal of the proteins of liver, steak, and kidney, which supplement both legumes and cereals, although they are of sufficient quality to promote growth and well-being in the rat over an extended period. Drummond reported that the nutritive values of the coagulable proteins of cod, herring, and salmon were quite as high as those of beef. Suzuki and associates, and also Mayeda, found that the muscle proteins of marine animals are sufficient to promote growth in rats, that all their proteins had about the same nutritive value as lactalbumin and better than casein, and that they were not lowered by canning Proteins of shrimp muscle and of whole clams, and to a less degree those of oysters, promoted growth in young white rats and were highly regarded for their nutritive value. Fellers found that the biological value of crab protein to be about the same as that of beef. In general, proteins of sea food are superior to most vegetable proteins in nutritive value, and the equal of most meat proteins. Moreover, flesh of fish is tender, savory, easily masticated, and highly digestible. Sherman points out 20 that lean fish and oysters are more digestible than lean beef; and fat fish, lobsters, and crabs were almost as digestible as ham and pork.

Fat fish contain vitamins A and B in appreciable amounts, and fish-liver oils are particularly rich sources of vitamins A and D. Vitamin C is reported to be abundant in roe of fresh-water fish. Some varieties such as canned salmon also contain vitamin G (or at any rate the pellagra-preventive vitamin) as shown by Goldberger in his pellagra-preventive work. Canned salmon also contains 2 to 8 U. S. Pharmacopoeia units of vitamin D per gram, a good amount. Tolle and Nelson report 25 that canned salmon contains from 6 to 15 percent oil, which compares favorably with cod liver oil as a source of vitamin D. At the time of their writing in 1931, they state that there was more vitamin D in the canned salmon sold in this country than in all the cod liver oil used for both human and animal feeding. Several other varieties of fish such as herring, sardines, and shrimp also contain vitamin D.

Oysters are good sources of vitamins A, B, and G. Whipple 26 showed that as they were removed from their beds their vitamin A content was about 3 units per gram, and their vitamin B 1 content 1.5 Sherman units per gram. The vitamin A content was slightly de-creased by cooking, but vitamin BI was not appreciably affected. There was only 0.05 U. S. Pharmacopoeia unit of vitamin D in the fresh oyster. Clams also contain a small amount.

Oysters and other food mollusks contain appreciable amounts of the easily digestible carbohydrate glycogen, chiefly in the mantle and body around the digestive gland. As much as 40 percent of the solid matter in ground oyster meats is soluble in water, including both organic and mineral constituents.

The oyster is equaled or excelled only by liver in the amounts of iron and copper (65.6 milligrams of iron and 48.3 milligrams of copper per kilogram) that it furnishes in an average serving of 110 grams.' This amounts to about 40 percent of the dietary standard of 15 milligrams of iron daily. These minerals are in a form easily available for blood-building purposes, and for treatment or prevention of anemia which responds to administration of iron and copper. The dietary combination of oysters and milk when fed to rats gave good blood regeneration, growth, reproduction, and lactation.

Sea food contains larger amounts of iodine than land products or fresh-water fish. Coulson shows 28 that the iodine content of haddock averages as high as 26,100 parts per billion, mullet 20,490, codfish 5350, and canned Chinook salmon 2010. According to the U. S. Bureau of Fisheries, oysters and clams contain about 200 times as much iodine as milk, eggs, or beefsteak. On account of this high content of iodine, sea food is particularly valuable in those inland sections of the country where ingestion of iodine is low and goiter is rather prevalent. Other minerals of great importance, such as calcium, phosphorus, manganese, copper, and iron, exist in marine products in relatively large amounts. Fish flour, which is a dehydrated product prepared from edible waste of certain fishery industries and which is suitable for use in human nutrition, contains from 8 to 28 percent of minerals, largely calcium and phosphorus.

Epidemiology. The literature contains numerous references to outbreaks of disease which have been attributed to consumption of fish, especially shellfish, produced under needlessly insanitary conditions. From 1815 to 1936, a partial tabulations reveals 50 epidemics lasting as long as 2 to 3 months, and involving "several" to 1411 cases each; and in addition, 64 epidemics lasting sometimes as long as a year, and involving from several to many thousands of cases each. By far, most of the cases were typhoid fever, although numerous outbreaks involved gastroenteritis, and cholera. This list incriminated oysters, clams, mussels, cockles, and butterfish. Other reports have listed numerous other outbreaks and many cases of diseases traced to infected or infested fish and shellfish, inadequately protected from contamination.

Shellfish themselves have no diseases of their own which they transmit to man. Man's pollution of shellfish-growing areas or his contamination of food in preparation for the market causes the, epidemics. These mollusks usually grow in relatively shallow waters of mild salinity near mouths of flowing streams. They subsist on food which is brought to them by the overlying waters. Inasmuch as much human sewage and land drainage finds its way to these streams, it follows that occasions arise when this pollution carries viable pathogenic microorganisms which infect the shellfish.

Oysters. The first clear case of the incrimination of such unsafe oysters was reported by Conn " in 1894. A typhoid epidemic was traced by a classic example of epidemiological skill to the consumption of infected oysters at a banquet at Wesleyan University. There were 25 cases with 4 deaths. This outbreak revealed to health officers that polluted oysters could be incriminated in an epidemic.

Numerous other typhoid epidemics have been attributed and sometimes traced to oysters, but between October 25 and December 20, 1924, the most serious outbreak on record occurred, involving more than 1500 cases and 150 deaths." The outbreak was most severe in Washington, D. C., Chicago, Ill., and New York, N. Y., although 10 other cities seem to have been affected and possibly 11 more slightly so. Although the oysters came from beds quite distant from sources of excretal contamination on shore, the waters were traversed by many boats with open toilets. Moreover, the oysters were "floated" or stored in pens alongside of the wharf and near boats with open toilets. It is highly possible that the oysters in these floats were infected. The abatement of the epidemic was attributed to the temperature changes in some bed, or the discontinuance of receipts from infected sources, or to the introduction of improved sanitary measures by the oyster producers on their dredging boats and in their floats.

The salmonella type has also been incriminated. Three men ate fried oysters in a restaurant in Washington. One man was taken ill immediately and another about an hour later, and both recovered, whereas the third man became ill several hours later and died. His symptoms were nausea, weakness, chilliness, and later great prostration. Salmonella schottmülleri was isolated from the stomach contents of the dead man and confirmed by culturing from a mouse which died from an inoculation with the stomach fluid. The oysters had a high content of the colon-group bacteria. Some investigators question this etiology. Stiles reported in detail a careful epidemiological investigation of a severe outbreak of 17 cases of typhoid fever (with 1 death) and 83 cases of gastroenteritis, caused by the consumption of infected oysters at the Minisink banquet at Goshen, N. Y., and a related out-break involving 10 typhoid cases and 16 gastroenteritis cases. One of the gastroenteritis cases, suffering from a chronic kidney disease, died, presumably from severe diarrhea, although in apparently good health for 3 days after the meal. Organisms of the colon group and Salmonella paratyphi (B. paratyphosus) were isolated from the oysters, which were clearly shown by epidemiological evidence to be incriminated. Stiles had previously shown that oysters and clams, grown in waters where inspection indicated that there was no serious pollution, were free from these types of organisms, whereas those collected from grounds showing probable pollution contained both types of organ-isms, and that bacterial quality of water was reflected in that of the shellfish. Fuller lists several outbreaks of gastroeneritis (presumably Salmonella infections), and also cholera from shellfish grown in polluted waters. Several outbreaks were caused by infection from typhoid carriers.

Botulism also seems to have incriminated oysters but only rarely. Hunter and Harrison mention outbreaks in which the central nervous system was affected, and death was due to suffocation. Several deaths from botulism recently have directed suspicion to imported canned clams, based on finding spores of C. botulinum in an empty can on the premises.

Mussels. Illness from the consumption of Pacific Coast mussels has been known since the days of the Indians. They observed that shellfish taken when ocean waves were luminescent, in hot weather, caused illness and death. Meyer and his associates 35 reported in 1928 that, since 1793, there have been recorded in the literature 244 cases of poisoning and 38 deaths from the consumption of mussels. Meyer further reports that in July, 1927, in the vicinity of San Francisco, there was a serious outbreak of mussel poisoning which involved 102 persons, with 6 deaths, and another in July-August, 1929, of 56 cases and 1 death. Murphy states that there have been 120 cases with 24 deaths in Europe in the last century, and that California has had 240 cases with 14 deaths in the past 9 years. He reports 2 deaths from eating cooked mussels from the Bay of Fundy, and that the poison is not present in all mussels of a given region nor are those in any region always poisonous. He describes the poison as a basic alkaloid, lethal to mice by the intraperitoneal injection of one-millionth of a gram. There is no known antidote. He agrees with Meyer that the toxic mollusk bears no characteristic feature to distinguish it from the non-toxic specimens. Sommer showed 38 that the poison is elaborated by Plankton of the genus Gonyaulax.

The same poison is also reported by Sommer 38 to be present in the sand crab. The ready availability of this animal for testing for the poison facilitates detection of the onset of the seasonal peak of poison production. Extensive research has shown that mussels—also clams 36 and crabs —contain a toxic principle in their digestive organs, especially during summer months. It has been extracted and studied pharmacologically, but it has not been identified chemically. One-quarter ounce of sodium bicarbonate per quart of water used for cooking mussels is reported to destroy over 80 percent of the poison in 20 to 30 minutes.

Dodgson lists numerous typhoid and paratyphoid outbreaks traced to shellfish. He gives a detailed description of mussel poisoning, and shows that it occurs in 3 types:

1. Erythematous—mild with quick recovery; probably anaphylactic.

2. Paralytic—always grave, often fatal; cause unknown, probably a toxemia.

3. Bacterially infective—mild to severe; typical of enteric infections.

Mussels, in common with other shellfish and fish in general, contain appreciable though variable amounts of arsenic and copper, but Dodgson states that there is no evidence that illness has been caused by these substances. He gives a detailed account of the successful operation and control of the mussel purification plant at Conway.

Fish. Several cases of poisoning by eating fish have been attributed to toxins produced by organisms similar to Clostridium botulinum, but very seldom to the salmonellas. Damon reports several outbreaks of typhoid fever caused by the consumption of infected uncooked fish. David Starr Jordan writes that certain groups of fishes in warm waters are poisonous by reason of toxic substances which are parts of their defense against enemies. When eaten by man, they produce the disease known locally as ciguatera, involving paralysis, characteristic pain at the joints, and gastric derangements.

Some species seem to be poisonous only when caught from certain localities, or at certain seasons, or at spawning time. Other fish become temporarily poisonous by their feeding on various forms of poisonous sea food. Jordan states that, during the Spanish regime, certain fish in the fish-market at Havana were listed as harmful and were prohibited for sale as food.

A tapeworm (Diphyllobothrium latum) may infect man from the eating of infested fish. In the infective stage, the parasite is in muscles and organs of fresh-water fish, particularly pike and perch. When these are eaten by man, encysted larvae are freed in the stomach and discharged into the small intestine where they develop into a tape-worm which may grow to a length of 6 to 30 feet. Symptoms may range from a simple gastric or nervous disorder to severe anemia simulating the pernicious type. Damon describes symptoms in anemia cases as exhibiting extreme pallor, weakness, cardiac disturbances, and ocular hemorrhage. These disappear with the parasites. Fish be-come infected by pollution of the streams with tapeworm eggs from feces of hosts. The disease has become established in the Great Lakes region, although cases seem to be increasing in the United States at large, particularly among women who taste uncooked fish in the preparation of "gefullte" fish. It has been pointed out that infested human excreta as well as those of dogs and other raw-fish-eating mammals are important factors in contaminating lakes with tapeworm ova.

Intestinal and liver fluke diseases in man are acquired by eating certain raw or undercooked fresh-water fish in the Far East.

Bacteriology of fish. An excellent review of the bacteriology of fish has been published by Griffiths. Fish are covered with a thin layer of a mucous substance, and this increases when the fish dies. It is composed of nitrogenous substances which facilitate the growth of numerous types of bacteria found in sea water and in fish feces. It is this slime which is so largely responsible for the bacterial contamination of fish packing-house equipment. Sanborn notes a marked similarity between the bacterial flora from the Atlantic and the Pacific fish.

Bacteria on and near the gills are an important source of infection that causes spoilage of fish and greatly increase the rate of bacterial decomposition. The intestines of fish do not contain a typical commensal flora, like mammals, but seem to depend upon the type of food ingested. When the fish is not feeding, the intestinal tract has been found to be free of bacteria. Although there is some disagreement as to whether the flesh of living or very recently killed fish is always sterile, there is general agreement that infection occurs soon after death. This can be reduced by thorough bleeding of the fish, removing the intestinal contents, and carefully cleaning the visceral cavity. Washing with chlorinated sea water or brine greatly improves the keeping quality. In general, the greater the number of bacteria in each gram of tissue, the greater the rate of deterioration and spoilage. Gibbons 46 found that, when haddock fillets are stored at temperatures as low as 0° F. (—18° C.), there is an initial decrease in their bacterial content, little change for a year, and then a slow decrease. A psychrophilic flora develops and predominates after long storage at 23° F. (—5° C.). Stewart showed that bacterial decomposition of iced had-dock proceeded much faster when it had previously been kept frozen than in fresh fish equally iced. Reay studied haddock frozen at 5.8° F. (—21° C.), held for different periods, and then thawed and stowed in ice, and found that the bacterial flora did not differ from that of fresh fish stowed likewise but that the thawed product deteriorated much more quickly.

Bacteria of the Escherichia and Aerobacter groups may be found in marine fish but seldom when the fish are taken far offshore. Escherichia coli is not a normal inhabitant of the intestines of fish. Its presence indicates that the fish were taken from polluted waters or were grossly contaminated in handling and marketing.

There are no bacterial standards for measuring quality of fish. Dependence for determining decomposition must rest on a combination of bacteriological, chemical, and especially organoleptic examination.

Bacteriology of oysters. When oysters become infected with typhoid bacilli, these organisms do not multiply but gradually die off. Jordan 48 floated oysters for 1 hour in sea water to which these organ-isms had been added, and then placed them in an icebox at 5° to 8° C. (41° to 46° F.). There was no multiplication, but the bacilli remained viable for 24 days. Tonney and White 49 placed typhoid bacilli in shucked oysters and studied their viability after storage at different temperatures. Those stored at 98° F. (37° C.) survived 1 day, those at 70° F. (21° C.) survived 4 days, and those at 45° F. (7° C.), 22 days. Living shell oysters were heavily contaminated with large numbers of the bacilli. Those stored at 70° F. (21° C.) survived 8 days in the shell liquor and at 45° F. (7° C.) 60 days.

Although pathogenic organisms have been isolated occasionally from oysters, this is too difficult and time-consuming for routine bacteriological examination. Much research has shown that the determination of organisms of the Escherichia-Aerobacter group, more recently only fecal strains of Escherichia coli, serves as a useful method for indirectly determining the presence of pathogenic organisms. The terms coliform or colon-group bacteria are used by bacteriologists to indicate any members of this group of microorganisms. Typhoid-fever bacteria live long enough in oysters to cause disease by the time that the oysters are consumed, and the coliform organisms live long enough to serve as indicators of possibly dangerous sewage pollution.

Hunter and Harrison report 17 that normal unpolluted oysters do not harbor Escherichia coli (Bacillus coli). Hunter and Linden, in confirmation of the work of Fellers and other investigators, found that bacterial flora of oysters consisted of organisms commonly found in water and soil. Inasmuch as coliform organisms are always present in intestines of animals and in soil, they are likewise always present in sewage, and to some extent in many surface waters. Their presence in oysters and overlying waters has heretofore generally been taken to indicate sewage pollution. However, this is not necessarily true, because it is known that some of these organisms may not come from intestinal contents at all but only from soil drainage. Coliform bacteria, particularly certain types of Aerobacter cloacae, are natural in-habitants of oysters, mussels, and barnacles, and may at times be found in enormous numbers and in complete absence of fecal pollution. For this reason, the new standard procedure of the American Public Health Association being proposed for the bacteriological examination of shellfish will be based on the use of only fecal Escherichia coli rather than on coliform bacteria in general.

These organisms are relatively easily determinable and therefore are useful indicators of the possible presence of sewage, even though the sewage may not actually contain disease germs at the time of sampling. Inasmuch as sewage always contains germs of intestinal origin, often those of typhoid fever, cholera, and dysentery, and always these fecal coliform types, it follows that the presence of these indications of sewage reveals too potential a hazard to public health to war-rant its toleration. In addition to this direct health aspect, sewage pollution is disgusting to consider as a contaminant of food.

It has heretofore been generally considered that, the greater the number of coliform organisms, the poorer the sanitary quality of the oysters. The mathematical expression of the degree of pollution has been called the score, calculated by adding the reciprocals of the greatest dilutions of 5 fermentation tubes that are positive to these organisms. A score above 50 was considered to be indicative of dangerous pollution, and warranted condemnation of the product. Total bacteria counts have not been found to have any regulatory significance, especially for shell stock.' The tendency now is to use only fecal strains of coliform organisms to determine sanitary quality (see pages 348 and 362).

Self-purification. Oysters "drink" large amounts of water by passing sometimes as much as 50 gallons (but more often nearer 10 or so) through their gills each day, depending on temperature. Oysters feed by the rapidity of the motion of the cilia on the gills and mantle in circulating the water, bearing their food, through their shells and digestive tracts. Bacteria are concentrated in the body, upon the gills, and in the shell liquor. In polluted waters, this bacterial content in the oyster may be much greater than that of the water in which the oyster is growing. When the temperature falls below 45° F. (7° C.), the shell closes, and the oyster ceases to feed or to collect the bacteria. Circulation becomes retarded but slowly forces the bacteria that are present into the digestive tract. Occasional opening of the shell allows their removal through fecal elimination. This cessation of feeding with attendant bacterial purification is called hibernation.

This self-purification of oysters has been utilized for cleansing stock that has been grown in polluted waters. When oysters drink large amounts of bacterially clean water, whatever bacterial content they had is washed out or eliminated in their feces. Hunter and Harrison report the results of several investigations which showed that oysters with high initial scores of 500-3200 reduced all of them to 41 or less (a score of 50 or less has been considered passable), scores of 5000 down to 14, and 410 to 32 in 5 days. This self-purification may be accomplished in as short a time as 24 hours if conditions are favor-able, such as: oysters are not too heavily contaminated at the start, water is clean, salinity and temperature are right, and there is free circulation of clean overlying water to carry away discharged polluted material.

Studies have been made to ascertain whether the oyster by these natural processes can actually eliminate a positive typhoid-fever infection. Krumwiede and his associates 55 heavily contaminated oysters by drinking them in sea water to which had been added feces containing Eberthella typhosa (the organism which causes typhoid fever). None of those organisms were found either in the oysters after the sixteenth and twenty-fourth days when the oysters were actively drinking at temperatures above 50° F. (10° C.), or in the sea water itself after the nineteenth and twenty-fourth days. This research showed that a period of about 3 weeks is necessary for an oyster to clear itself.

Mussels and clams are also successfully treated by this self-purification process.

Chlorine treatment. Great success in purifying unsafe water sup-plies with chlorine led Wells to treat infected oysters with chlorinated sea water. He depends on chlorination to sterilize the overlying water, the exterior of the shells, and the material excreted from the oyster. Krumwiede, Park, and their associates again heavily contaminated oysters by drinking them in sea water contaminated with feces containing Eberthella typhosa, and then treating them in tanks of water containing initially as much as 35 p.p.m. of chlorine. They found that chlorination treatment greatly reduced the number of these organisms but was ineffective to kill all of them and to make such contaminated oysters safe for food. However, Wells holds that this treatment is to be considered as effective only for sterilizing everything exterior to the shells and for enabling oysters to eliminate contaminating substances by their natural functions, and that the process should be considered as according a factor of safety in prevention of recontamination when oysters are floated for conditioning for marketing. The process should not be depended on to make badly contaminated oysters safe, but it assures conditions of sanitation under which the oyster can remove any slight pollution through its natural functions. Hunter and Harrison maintain that it is as reasonable to apply chlorine to oyster treatment as it is to treat our supply of drinking water. It should be noted that chlorine does not enter the oyster but acts only to provide clean water in which the oyster washes its body.

A large number of outbreaks ascribed to oysters have been due to floated oysters which were stored in polluted waters. (The holding or storing of oysters in water is called "floating.") Experience in Europe teaches that greater use of controlled cleansing plants has reduced illness from infected shellfish. The difficulty of adequately policing a contaminated and closed area is leading health officials to favor some sort of controlled cleansing in order to minimize danger from polluted shellfish and to accord facilities to use stock which otherwise may possibly be used surreptitiously anyhow by unscrupulous operators. This treatment is particularly urged for the processing of shellfish for the half-shell trade.

Bacteriology of Crustaceans. Fresh crabmeat furnishes a particularly favorable medium for bacterial growth. The flesh of crustaceans is sterile or nearly so when it is freshly cooked. Any bacterial growth represents contamination by handling the products. Hunter reports 58 that certain experimental work and extensive experience have demonstrated a relation between insanitary methods of production and incidence of fecal Escherichia coli in the finished product. The presence of these organisms indicates contamination with filth, potentially dangerous to health. Organisms of the colon-aerogenes groups, not strictly fecal in type, do not indicate health hazards but they do signify that the product was handled in an unclean way. It has been shown to be entirely possible to operate a plant so that the product will be free from any fecal types of bacteria.

The presence of large numbers of aerobic bacteria is the result of contamination picked up in preparation of the product for shipment, possibly increased by multiplication. Therefore, the total count indicates degree of cleanliness and refrigeration in plant operations and shipment.

Decomposition. Decomposition of such nitrogenous foods as meat, poultry, and eggs has its counterpart in decomposition of fish and shellfish. Soon after fish die, the flesh becomes stiff and passes into the condition of rigor mortis. Fish in this condition are always strictly fresh. Even though they may be well iced, fish soon become stale and begin to deteriorate. The flesh becomes soft and flabby, and a strong fishy smell develops.

Deterioration and spoilage of sea food can be followed by determination of characteristic chemical changes, such as formation of carbon dioxide, methane, hydrogen, amines, ammonia, volatile acids, and other compounds and products. These substances are not constant in their qualitative and quantitative relations by reason of the variation in the factors which bring them about, such as composition of the food itself, temperature, type of bacterial flora, technological processing, time intervals, and also the kind or amount of food of the fish.

Enzymic. Agents directly concerned in these changes are enzymes which occur naturally within the body of the fish, and microorganisms which invade the tissue from outside, mostly from water and plant equipment. Inasmuch as fish are cold-blooded animals, their metabolism must be able to function effectively at temperatures where warm-blooded animals die. These enzymes of fish are potent at 32° F. (0° C.), and are still active at much lower temperatures. Their chemical effects are to break down complex proteins (and carbohydrates, as in oysters) into simpler peptones, polypeptids, amino acids, and ammonia. Tressler showed that determination of amino-acid nitrogen is a good index of the rate of decomposition of protein.

Bacteriological. Gibbons and Reed showed that, when pure or mixed cultures of bacteria were inoculated into fresh tissue, there was a rapid breaking down of protein and a great increase in production of ammonia. Fellers found that spoiled raw salmon contained high bacteria counts and a high indole content. Certain types of bacteria liberate hydrogen sulphide from proteins, and Almy found that more is liberated from stale than from fresh canned fish. Fellers showed that the quantitative determination of indole or ammonia does not measure spoilage because degradation from these bacterial sources may occur only many hours after autolytic changes have taken place. Nickerson and Proctor 60 made extensive tests on changes in sterile and non-sterile haddock muscle, held at temperatures of 32° F. (0° C.) to 63° F. (17° C.). They found that contaminated muscle underwent greater changes, as measured by the amino acid and especially by the ammoniacal nitrogen, than sterile muscle. Even when the fish was stored at 63° F. (17° C.) for 24 hours, the ammonia content was not high but thenafter became increasingly important. This work demonstrates that bacterial decomposition is in addition to the autolytic enzymic effect, and that refrigeration is necessary to keep bacteria growth from contributing to spoilage. Initial autolysis provided the microorganisms with nitrogenous food in readily available form.

Measurement. The determination of the amount of volatile nitrogenous bases in codfish muscle is recommended by Beatty and Gib-bons 61 as a useful measure of spoilage of fish. They state that between the pre-rigor stage and the first appearance of odor, there is an increase of 6 milligrams of these volatile bases per 100 grams of tissue, but the value for fresh fish must be known in every case be-cause of wide variation between samples. Boury and also Kimura and Kumakura confirm the significance of these volatile nitrogen bases. Lucke and Geidel state 64 that, in all types of fish investigated, a value of about 20 milligrams of volatile basic nitrogen per 100 grams of flesh was found; that when it had increased up to 30, the keeping quality was lessened and shipment was not warranted; and that at 50, the fish was altogether spoiled.

This combined effect of autolytic enzymes and microorganisms to cause deterioration of fish has been clearly shown by Stansby and Lemon to consist of two definite stages designated as primary and secondary. The former is enzymic, and is concerned with the hydrolysis of proteins to amino acids or to their intermediate polypeptids or peptones. The secondary changes are bacterial in nature, and are concerned with production of disagreeable flavors or odors from ammonia, amines, indole, hydrogen sulphide, and skatole, accompanied by a decrease in the hydrogen-ion concentration. As a result of primary changes, the flesh becomes softer, and sometimes exudes a "drip" of dissolved proteins, amino acids, and minerals. These changes entail a loss of freshness. Secondary changes follow, and cause the offensive odors of ordinary decomposition. These investigators have devised a method to measure both these stages. The primary changes are measured by titrating buffer capacity, and the secondary changes by titrating ammonia. This work is particularly useful for measuring deterioration (primary changes) before decomposition becomes organoleptically evident (see description of method on page 359).

Fat. Fat in fish which has been cold stored for a long time and not sufficiently protected from attack by atmospheric oxygen becomes rancid and imparts to the flesh a dark color described as rust. This condition can be chemically measured by titrating the oil for its free fatty acid, and by determining the peroxide number. Stansby found 66 the following peroxide values for several degrees of fat deterioration:

Fresh 0–0.6

Slightly rancid 0–21 .4

Rancid 18.4–36.5

Extremely rancid 33–201

He confirmed the significance of this determination by tests on "floated" fish kept by dealers in iced sea water in water-tight barrels until sold. Peroxide values were lower for this floated fish than for fresh fish in ice, because they were protected from air (retarding oxidation), but their bacterial decomposition and content of free fatty acids were much greater.

Oysters. Spoilage of oysters has been excellently discussed by Hunter and Harrison. Oysters in the shell kept in a cool place will remain alive and edible for comparatively long periods. Out of water, the shell is mostly kept closed, although it may open slightly from time to time. When the oyster dies, the shell opens, and the oyster meat decomposes rapidly, contaminating the entire lot in the container.

Oysters die soon after shucking. Inasmuch as they contain both protein and carbohydrate (glycogen), their decomposition involves both putrefaction (as in meat and fish) and fermentation (as in sugar and milk). The glycogen is hydrolyzed to form reducing sugars, and these are fermented to form mainly lactic acid. Decomposition of shucked oysters is due in the beginning to water and soil bacteria (producing red and blue-green pigments), and to members of the Proteus, Clostridium, Bacillus, Aerobacter, and Escherichia groups. Later, spoilage is increasingly caused by streptococci, lactobacilli, and yeasts. Autolysis is also concerned in oyster spoilage. It is probable that both putrefaction and fermentation proceed together, and are caused by ordinary water and soil bacteria, together with such intestinal types as occur in whatever sewage is present.

In an effort to find a laboratory method for the detection of incipient decomposition (or spoilage before it becomes evident to the senses of sight and smell), Hunter and Linden 67 found that good oysters had as many as 30,000,000 aerobic bacteria per milliliter of oyster liquor whereas others in a state of incipient decomposition had only 12,000. Hence, there was no correlation between the condition of the oysters and their microorganic content. However, these investigators did find that the determination of the hydrogen-ion concentration in oyster liquor served to distinguish oysters as good, stale, slightly sour, and sour. Spoilage is retarded by reducing the number of organisms by thoroughly washing the oysters, and especially by maintaining temperatures below 45° F. (7° C.) by means of ice. Ice should not be in direct contact with the oysters because ice water would adulterate the oyster liquor, but it should be packed around the container during shipment and storage.

Green oysters have been shown to be colored by absorption of colloidal copper or copper salts from water, and by ingestion of diatoms. Color from copper is distributed in streaks or patches over the liver or visceral part, and sometimes gives a greenish tinge to the whole body. No deleterious effects are known to have been caused by eating such oysters. When oysters have fed on green diatoms, their gills become colored a dark olive-green, suggestive of chlorophyll. These microscopic plants themselves are not harmful to health, and oysters which have fed on them are not injurious from this cause.

Pink oysters have been shown by Hunter to be infected with a yeastlike fungus. This yeast has been tested on laboratory animals and found to be non-pathogenic, and there is no evidence that it will render oysters injurious. The organism contaminates equipment of fishing boats and particularly shucking houses. Inasmuch as it does not develop until several days after packing, the presence of color indicates that oysters are not strictly fresh, although they may not be actually spoiled. However, during this time other organisms have probably grown also, and therefore such oysters should be carefully examined for evidence of decomposition.

Effect of cooking to destroy infection. Hunter and Harrison discuss the work of Clark who infected oysters with Escherichia coli and streptococci by floating them in sea water to which sewage had been added. These oysters were then stewed, fried, and escalloped.

When the oysters were placed in cold milk and heated, all organisms were killed by the time the milk boiled, but when they were added to boiling milk, the organisms were not killed until boiling had continued for at least 5 minutes. Frying for 2 minutes killed most of the organisms, but some survived frying for 8 minutes. Escalloped oysters were sterilized by cooking at oven temperatures for 15 to 30 minutes. Stiles showed that coliform organisms in naturally infected shucked oysters were killed by 5 to 10 minutes' exposure to live steam, and that heating for at least 10 to 15 minutes was necessary for clams and oysters in the shell.

Pasteurization of oysters is not practical. A temperature of 122° F. (50° C.) cooks the oyster, but is too low to kill pathogenic organisms. Even when stock was heated in brine at a temperature of 158° F. (70° C.), dangerous bacteria were not killed.

From such data, it is seen that ordinary cooking cannot be relied upon to render oysters safe when they have become contaminated with pathogenic organisms.



Fish, shellfish, and crustaceans, whether fresh or preserved by any of the several methods, have been found on the market in various stages of spoilage. Shrimp and crabmeat have been packed under insanitary conditions and sometimes when they showed signs of de-composition. Oysters have frequently been adulterated by the addition of water. Oysters and clams have both been incriminated in out-breaks of infectious disease from sewage pollution or contamination from carriers. Mussels have caused toxemia. Parasites in fish have spread to man. Artificial color has been used for smoked fish, and borates and benzoates have been used to help preserve salt fish.


Physical examination. If oysters are almost white, have a soft spongy texture, are almost devoid of saline taste, and yield a thin watery liquor on draining, they were unquestionably adulterated with water. An excess of 5 percent of drained liquor from shucked oysters indicates watered stock.

Shell stock is prepared for analysis by washing the shells in potable water, and shucking them to yield at least 1 pint of drained meats, draining on a specified type of skimmer, removing any piece of shell, and storing in a proper container. Shucked stock is well mixed by pouring back and forth. The amount of free liquor is determined by draining on a skimmer or strainer for 1 minute. Samples are kept at temperatures of 1° to 10° C. (34° to 50° F.).

Chemical examination. Total solids. A 10 gram sample of the ground meats and liquor is evaporated just to dryness, dried 4 hours in a water oven, cooled in a desiccator, and weighed promptly.

Chlorides. The chlorides may be determined by digesting with silver nitrate and titrating with ammonium thiocyanate. They are re-ported as sodium chloride.

Ash. The weighed sample is ashed in a muffle below dull redness, cooled in a desiccator, and weighed.

Acidity. A sample of 25 milliliters of the clear liquor is titrated with 0.1 N alkali to the end point of phenolphthalein. In fresh oysters, the acidity is equivalent to 1 to 2 milliliters of N/10 alkali per 100 milliliters of liquor.

Hydrogenion concentration (pH). The spoilage of oysters is accompanied by a change in the pH value of the oyster liquor. This is determined by testing a drop of liquor on a porcelain plate with a series of indicators. A pH of 6.1 to 5.6 indicates a zone where the oysters are passing from good to stale; the zone 5.3 to 4.9, stale to sour; and below 5.0, advanced decomposition.

Bacteriological examination. Samples of overlying waters are examined bacteriologically according to Standard Methods of Water Analysis, published by the American Public Health Association. One or more tubes in 10, 1, and 0.1 milliliters should be determined for each sample. For the examination of shellfish (including both meats and liquor), amounts of 1, 0.1, and 0.01 milliliters are employed. The results are expressed in terms of the most probable number of coliform organisms per 100 milliliters of sample. This method also seems to be applicable for other edible mollusks such as clams and mussels.

Until recently, the scoring system (see page 349) was generally used. It is falling into disfavor, and has become obsolete in Canada and in Maryland."

The total bacteria count on shucked stock while in the plants has been found useful to determine the cleanliness of the methods used, but it does not have much significance in interstate shipments because the counts do have significance only when they are known on the same sample both before and after shipment or other handling.


Bacteriological examination. Various chemical methods have been tried but found to be unsatisfactory for the determination of sanitary quality in crabmeat. The only method found useful is the bacteriological examination.

For the determination of Escherichia coli, a known weight is shaken with sterile glass beads in a sterile salt solution or water, inoculated into standard lactose broth, and incubated at 37° C. (98.6° F.). Positive presumptives are streaked on plates poured with Levine's eosin-methylene blue agar. From these, typical fecal-type colonies are transferred to agar slants and identified.

Total bacteria counts are made on the suspension just described by using standard nutrient agar and incubating at 37° C. (98.6° F.).


Physical examination. Anderson has described in great detail 71 the organoleptic tests by which decomposition of fish can be recognized. His points are summarized as follows:

1. Rigor mortis. This condition persists longest near the tail. The flesh is firm and elastic to the touch. Its presence is a guarantee of freshness. The flesh is acid during rigor and becomes alkaline when rigor passes off. If the flesh has become soft and inelastic, and pits on pressure, further evidences of decomposition should be looked for.

2. Reddish discoloration. When the flesh around the backbone assumes a reddish color from the diffusion into the meat of decomposed blood cells, the flesh is not strictly fresh. The intensity of this discoloration indicates the length of time since the fish was captured.

3. Odor. Strictly fresh fish do not smell fishy. When the odor has a spoiled taint passing to putridity, the fish is unwholesome. Sometimes the covering slime may smell offensive but its washing off may reveal that the fish itself is wholesome.

4. Removal of flesh. In fresh fish the flesh is stripped with difficulty from the backbone. If it comes away readily, this indicates a degree of decomposition.

5. Abdominal cavity. The kidney, located anteriorly and ventral to the backbone, is a diffuse friable vascular organ which breaks down in 24 to 48 hours to a reddish brown debris while the fish still may be quite fresh. If the abdominal walls are firm and elastic with no discoloration or fish smell, the fish is satisfactory. If they are soft and pulpy with appearance like apple-jelly, are discolored, have a tainted odor, and are alkaline to litmus, the fish should be condemned if other inspection is supporting.

6. Gills. The gills of fresh fish have a reddish ground color which turns gray and slimy after the third or fourth day. The degrees of redness of fresh gills are quite variant.

7. Eye. The eyes of fresh fish are prominent with jet-black pupil and transparent cornea. In about 24 hours, opalescence begins in the cornea and a lack-luster in the pupil. In 3-4 days, the eyes are gray and shrunken.

8. Scales. The scales of stale and decomposed fish have lost their sheen and rub off easily.

Chemical examination. Although a large amount of research has been directed to finding laboratory methods for the detection of incipient decomposition in fish, none of them have been developed to the degree of general acceptance. One of the most promising is the method of Stansby and Lemon. They utilize the determination of buffer capacity to measure the deterioration of the protein content, and the titration of ammonia to measure the bacterial decomposition. Their work was done on haddock; other investigators are applying these methods to other fish.


There is a tendency to consider that, inasmuch as the marketing of fish is a messy operation, no great care need be given to sanitation. Such an attitude is apparent to anyone who visits fish markets in large population centers. Approach to them is usually indicated by a strong fishy smell, and by the indifferent condition of equipment and its housing. Fresh fish do not smell fishy. Therefore, this strong fish odor clearly indicates the presence of decomposing fish products.

In addition to this general insanitation of plant, there is often a tendency of vendors to neglect to practice principles of personal hygiene in their handling of fish. Fish are not always given the degree of sanitary consideration that should surround the handling of a food. Fish should be handled with the same care as any other food. Equipment should be constructed of materials that are impervious to absorption of liquid from the fish drainage. All utensils, benches, tables, tubs, receptacles, and in fact, every piece of equipment that comes in contact with fish should be thoroughly cleaned daily to the degree that slime, refuse, and even the smell should be completely eliminated. The market stalls and stores, including the floors, ice-boxes, and drains, should be kept in good repair to facilitate complete cleaning and draining. The rising cost of other foods and the increasing availability of sea food indicate an expansion in the consumption of sea food which would be facilitated if insanitary hindrances were remedied. The merchandising of foodstuffs in general is largely built on appeal to the senses, and in this respect the usual marketing of fish is far behind the times.

With regard to the supervision of the shellfish supply, laboratory examination of samples of oysters is sometimes useful, but it does not give information concerning the sanitary quality of the stock sufficient to constitute adequate public-health protection. Supervision must start with the examination of waters from which shellfish are taken, and extend through the handling and distribution practices until the stock is delivered to the ultimate consumer." As a result of the severity of the 1925 outbreak of typhoid fever traced to oysters, a conference of health officers, food-control officials, and oyster packers agreed that effective sanitary control of the industry required the following essential provisions:

1. The oysters should come from beds which have been found to be free from pollution and disease-producing organisms.

2. The conditions of storage, handling, and distribution should protect the food from contamination with pathogenic organisms and deterioration or adulteration.

3. Careful epidemiological studies should be made of any disease outbreak which incriminates shellfish.

In order to express these provisions in a control program, it is necessary that the respective states should supervise the sanitary quality of waters over shellfish beds and designate only those areas from which stock may be taken. This requires a sanitary inspection of the watershed, sources of pollution, estimates of time required for the pollution to pass from place of entry to oyster-growing area, effects of dilution, tidal action and currents, influence of bottom topography, examination of samples of water and oysters, and adequate policing of closed areas.

Although many states require a formal certificate showing that each employee has been given a compulsory medical examination and found to be free from communicable disease, there is a tendency now to discount the value of this practice. The emphasis is increasingly educational. The employer is expected to examine all applicants for employment in a shellfish plant for open lesions on hands, arms, or face, and to question them relative to evidence of previous typhoid or paratyphoid fever; if such evidence is found, the applicants are referred to a laboratory for examination.

Records must be kept of sources of all oyster receipts and also destination of all shipments. This stock must be packed in clean barrels and sacks, and marked to identify the shipper. Receivers keep a record of all shipments received. Temperatures must be kept below 50° F. (10° C.) but above freezing. Shucked stock must be packed in clean, sterilized containers, sealed to prevent tampering. Only those types of containers may be used which can be thoroughly cleaned; non-returnable containers are preferred. Containers shall be marked to identify the shipper, and maintained at a temperature as above.

Retailing should likewise be conducted by persons who are not carriers of pathogenic organisms. Stock must not be openly displayed, and proper refrigeration must be continuously applied. A record should be kept of all lots, showing from whom they were received.

A reasonably safe product is assured by the certification plan. This procedure provides that health authorities in the producing states exercise sanitary supervision over the industry by requiring that stock be produced and handled as above outlined and that certificates be issued for all shipments that comply. The U. S. Public Health Service checks on the effectiveness of the enforcement by the respective state control officials. If this is satisfactorily done, the Service endorses these certificates, and distributes the information in semi-monthly releases throughout the country and to Canada by the state and local health authorities. This procedure enables every shipment to be traced from source to retailer. Unfortunately, many health authorities in the inland territory are reported as not paying much attention to these lists. This indifference jeopardizes continuance of this control.

Regulatory authorities have assumed that where the contamination of overlying waters, as shown by their bacteriological examination, was probably of human origin, and where more than 50 percent of the 1-milliliter portions were positive in coliform organisms, they were warranted in prohibiting the harvesting of shellfish directly from such areas for market purposes. This has been shown to be equivalent to a most probable number of about 150 coliform organisms per 100 milliliters of sample. There is often a zone between clean and condemned areas where contamination is slight enough to warrant operation of some approved cleansing procedure. The offshore boundary is marked by the line in which 50 percent of the samples of 1-milliliter portions are positive. The inshore line is marked by 50 percent of all samples positive in 0.1 milliliter portions of the overlying waters. It is believed that clams and oysters inshore of this latter line are in waters too polluted for safe treatment.

Oysters may be removed from moderately polluted areas in the closed or active feeding season and relaid in a large body of clean water, not less than 15 days before the opening of the next season, in order to give the oysters time to cleanse themselves, provided that adequate policing can prevent the unscrupulous sale of the untreated stock. The fishing boats themselves must be inspected to insure that proper sanitation precludes dangerous or offensive contamination. Proper storage facilities must be provided to keep the stock from spoiling. The producer must furnish the receiver a true record of the sources or areas from which the shellfish were taken, and this list must be subject to inspection by the official state agency. The stock may be "floated" in waters of proper salinity and free from pollution.

Shucking and packing plants should operate under a permit from the official control agency, and should be located, constructed, and operated in accordance with recognized standards of sanitation and cleanliness, such as adequate light and ventilation, proper washing and sterilizing facilities, plenty of clean water and steam, sanitary toilets and lavatory facilities for the workers, protection against flies, sanitary disposal of refuse, installation of equipment that can be cleansed and sterilized daily, and health supervision of employees to avoid employment of diseased persons or carriers.

The content of Escherichia coli in shellfish freshly removed from the beds is roughly indicative of the sanitary condition of the over-lying waters. As these organisms do not multiply in shell stock, their content is a fair index of the condition of the waters. On the other hand, the shucking of oysters may greatly increase their numbers by contamination from the utensils and hands of the shuckers, as well as by multiplication in the shucked stock, facilitated by temperatures above 60° F. (16° C.). A high content in shucked stock may mean: (a) a polluted source, (b) unclean packing, (c) contamination after packing, (d) inadequate refrigeration. Therefore, a high Escherichia coli count in fresh shellfish indicates probably gross sewage contamination, but in shucked stock may or may not indicate such a health hazard. Reliance must be placed on inspection and sanitary control of the beds and packing-house operations, as well as on the bacteriological examination of shell and shucked stock at the shucking plant 75

The Baltimore Health Department has drawn up rules and regulations 76 for the sale of shellfish based upon these recommendations. The Maryland State Board of Health has issued detailed information for harvesting, packing, and shipping oysters, together with sample copies of application forms, plans of approved type of oyster houses, and requirements of the City of New York, the State of Illinois, and the Dominion of Canada for the importation of oysters 77

Several states have enacted laws and promulgated regulations to eliminate dangers from floated oysters.' Virginia prohibits the practice. Maryland and Connecticut require that floated stock be labeled to declare this treatment. New York has surrounded the practice of floating with very restrictive requirements (specific gravity of the water to be 1.007 and compliance with the 1914 drinking-water requirements of the U. S. Treasury Department). Self-purification plants in Massachusetts are operated under the control of the State Department of Health. The Florida State Board of Health has drawn detailed rules to regulate collection, handling, shucking, packing, and shipping of oysters, scallops, and clams. Stock must come from unpolluted waters or be transplanted to clean waters not less than 15 days prior to the next market season, may be floated in unpolluted water of salinity equal to that of the growing area, and may be shucked, handled, and sold only in plants which have been licensed by the State Department of Health and which comply with detailed requirements of sanitary construction and operation.

Seasonal increase in the toxicity of mussels on the California coast is under the surveillance of the State Department of Health. Samples of mussels from producing areas are systematically examined for signs of rise in incidence of toxicity. When they are dangerous, their sale is forbidden s6

The recent "sea food amendment" to the U. S. Food and Drugs Act (designated as Sec. 10A of the Act) authorizes the Secretary of Agriculture to assign inspectors to supervise plant operations of any packer of sea food who applies for this service, pays the costs, and agrees to comply with sanitary, labeling, and other requirements. When cans are packed under these conditions, the labels bear the statement "Production Supervised by U. S. Food and Drug Administration." This supervision prevents possible violations at the source and is permissive, not mandatory 79

In order to pack crustacean products free from the fecal type of organisms, it is necessary to exercise simple hygienic precautions. Meat and utensils must be kept protected from exposure to foot traffic, to flies, to handling by unclean employees, and to primitive or other-wise insanitary toilets. Utensils must not be placed on the floor or nested so that bottoms contaminate insides of others where meat is to be packed. Employees should wash their hands. All equipment should be made of metal which is readily cleanable and effectively sterilized. All utensils should be thoroughly cleaned after, and sterilized before, each use. Floors and benches should be built of non-porous material free from cracks where dirt and microorganisms can collect. Premises should be adequately lighted to enable employees to see how and what to clean. Plenty of clean water and steam should be available. By practicing such more or less obvious measures, it is possible to pack crustaceans free from harmful organisms or from Escherichia coli. This is the standard now being met in commercial practice.

As the result of application of measures of sanitary control out-lined above, the fish and shellfish industries have taken long strides away from old conditions which obtained when these products were incriminated in outbreaks of disease and when they were contaminated from their insanitary surroundings. Industry and officials have worked together to prevent a repetition of the various troubles of the past, and to give the public the best sea food possible under existing trade conditions. Products are effectively controlled from the sources and through the packing operations into the channels of trade. The industry is now on a plane of sanitary excellence, and the public can use this valuable food with confidence in its wholesomeness.


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56. C. KRUMWEIDE, W. H. PARK, and associates, ibid., 16, 142 (1926).

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58. A. C. HUNTER, Am. J. Pub. Health, 24, 199 (1934).

59. N. E. GIBBONS and G. B. REED, J. Bact., 19, 73 (1930).

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66. M. E. STANSBY, J. Assoc. Offic. Agr. Chem., 18, 616 (1935).

67. A. C. HUNTER and B. R. LINDEN, Am. Food J., 18, 538 (1923).

68. Anon., J. Assoc. Offtic. Agr. Chem., 20, 70 (1927).

69. Reprint 1621, Pub. Health Repts., March 23, 1935, quoted from Reference 57.

70. C. A. PERRY, American Public Health Association Year Book 1935-1936, p. 111.

71. A. G. ANDERSON, 26th Ann. Rept. Fishery Bd. for Scotland, 1907. Part III,

pp. 11-39. Also abstracted in U. S. Bur. Fisheries Spec. Mem. 1061A, 1935.

72. G. A. FITZGERALD and W. S. CONWAY, JR., Am. J. Pub. Health, 27, 1094 (1937).

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74. CROHURST and SULLIVAN, "Chesapeake Bay Study," U. S. Pub. Health Service (mimeographed), quoted from Reference 57.

75. L. M. FISHER, Am. J. Pub. Health, 26, 364 (1936).

76. "Regulation Governing the Distribution and Sale of Oysters and Clams," Baltimore Health News, 13, 45 (1936).

77. Manual for Oyster Packers, Bulletin Maryland State Dept. Health, 1929.

78. Revised Regulations for Inspection of Canned Shrimp, Effective July 1, 1936,

Food and Drug Administration, U. S. Dept. Agr., June 15, 1936.

79. Report of the Chief of the Food and Drug Administration, 1935, p. 13.

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