( Originally Published 1939 )
Dairy farming. The production of milk is becoming a vocation which requires well-trained personnel and adequate equipment. The increasing sanitary requirements are making it difficult for the farmer to meet the quality standards unless he gives detailed attention to milk production. He cannot do this if his milk operations are only an incidental sideline to his general farming program. The specialized knowledge requisite to produce milk of satisfactory quality, the necessity that the dairy herd be tuberculin tested and otherwise healthy, the requirement for adequate equipment ranging from type of barn to milk strainer, all operate to convert the milk producer into a dairy-man whose main business is to produce milk. To make such an undertaking profitable, the dairyman is engaging in larger and larger operations so that it is common to see dairy farms provided with milk equipment comparable to that of many city milk plants, and conducted on a businesslike basis. This requires a capital investment which conduces to managerial responsibility. The conversion of the erstwhile poorly equipped milk producer, who shipped milk when he had any, into a capable dairyman has very largely contributed to the great improvement in the quality of our present-day milk supplies.
Permit. In general, any person, firm, or corporation who engages in the milk business must operate under a permit issued by the health officer of the respective community. The permit system is administered according to two general procedures: (a) every farmer must be under a direct license from the health department, or (b) every farmer is permissively allowed to ship to a licensed dealer as long as he complies with the local regulations of the community which uses his milk. The difference between the two practices lies in the placing of the responsibility for enforcing compliance with the law: in (a) it is with the health officer directly, whereas in (b) it is with the locally licensed dealer. This dealer jeopardizes his own permit if he accepts milk from producers who do not comply with the local requirements.
Under either the (a) or the (b) procedure, the farmer who wants to ship milk applies for a permit from the health officer or makes application to a licensed milk dealer to be taken on as a regular milk shipper.
Inspection. After the application is filed, a dairy farm inspector visits the farm to check on its equipment and its degree of compliance with the regulations which govern the conditions under which milk may be produced and shipped. The inspector and the farmer go over the premises together. If any part does not comply, instructions are given as to how to remedy the condition. The farmer is instructed in the proper handling of milk, cleaning of utensils, and care of the herd. The principles of sanitation in milk production are explained. In the more progressive departments, the farmer is shown by actual demonstration how milk should be produced and the equipment handled.
Herd. A fundamental axiom in dairy husbandry holds that a dairy cow is no better than her udder. This is a highly developed gland, susceptible to numerous diseases, injuries, and infections which damage its usefulness in the production of milk 1 and sometimes cause disease in the human beings who consume it. Usually when an abnormal condition is observed, it is advisable to consult a veterinarian.
A milking herd must be kept in a healthy condition. The interpretation of this requirement varies over a wide range. All inspectors agree that every cow must at least look healthy. Many municipalities require that the herd shall be tuberculin tested and kept free from tuberculosis under the federal and state cooperative eradication pro-gram. The federal and the state governments have undertaken a joint program for the eradication of tuberculosis, paratuberculosis (Johne's disease), and Bang's disease from cattle. These official agencies and the owner contract for a testing procedure which involves the condemnation for slaughter of any animal which reacts to the respective tests. Each agent pays one-third of the difference between the appraisal value of the animal and its salvage value. The tuberculosis-eradication program provides an individual accredited herd plan, and a modified accredited area plan. A tuberculosis-free ac-credited herd of cattle is one in which the entire herd has passed two negative successive annual physical examinations and tuberculin tests. Under the modified accredited area plan, a given area is declared to be an official modified tuberculosis-free accredited area if the total number of reactors is less than 0.5 percent of all the cattle within the area' Official certificates are issued to cover each animal which is in such a herd.
Paratuberculosis or Johne's disease (caused by the Mycobacterium paratuberculosis) is a highly infectious bacterial dysentery' occurring in practically every state. It is spread from diseased to healthy animals by infected pastures, feed, and drinking water. The presence of the disease may be detected by the johnin test, used in a similar manner to the tuberculin test. The federal government pays indemnities to cattle owners for reactors on the same basis as for tuberculous cattle.
Infectious abortion or Bang's disease, caused by the Brucella organisms, is widely prevalent among dairy herds. It not only exacts great economic losses in livestock but also causes undulant fever in man (see page 38). Definite programs are being developed to control the disease. By means of the agglutination technic, reactors can be detected for removal from the herds, and the process repeated until no more cases appear. All new purchases must be made from clean herds.
Mastitis is an inflammation of the udder, widely prevalent in dairy herds. It may be caused by non-infectious agents such as bruises, injuries of the udder or teat, severe machine-milking, and chilling, none of which leave permanent injury. However, possibly 90 percent of the cases of mastitis are caused by infection with micro-organisms, chief of which is the Streptococcus agalactiae. This organism is non-pathogenic to man, but there are other strains, such as the Streptococcus epidemicus, which are extremely virulent (see page 37). Infectious mastitis does not heal without leaving permanent injury to the udder with more or less alteration in the composition of the milk.' In the udder there is a thickening of the connective tissue which can be recognized by palpation. It greatly de-creases milk production, and when severe it changes the composition and appearance of the milk. Mastitis milk may have a high pH value (greater alkalinity than normal milk), casein clots, high leucocyte count, a chloride content above 0.12 percent, and other changes. Although bacterins have been developed for the treatment of infected herds, the most promising procedure for control of the disease is the segregation and disposal of reactors from tested herds and their replacement with clean animals.' Mastitis is often transmitted from animal to animal by milking machines whose teat cups have become infected. Detailed instructions for the examination of infected animals have been published for the guidance of dairymen.
Inasmuch as mastitis may injure an udder permanently with attendant atrophy of the teat, some municipalities stipulate that no milk will be accepted from any cow that has less than four normal teats.
Abnormal milk. Milk that is produced near parturition is abnormal in composition. Common practice requires that milk shall not be used that is produced fifteen days before and five days after the cow has calved. Almost everyone agrees that such a requirement is desirable if it can be enforced. Farmers who do not give their cows much rest may find that they have been milking right up to the time of delivery. Good dairy practice rests the cow for about a month prior to the time of her expected delivery, and this allows ample leeway in case of miscalculation.
Equipment. Equipment for the production of high quality milk, together with the technology of its proper handling, has been highly developed and publicized. Most of the intelligent and conscientious dairymen utilize this information effectively, but many producers are careless and more or less indifferent in their practices. This non-compliance with approved technology usually results in the production of low quality milk, although it is possible to produce a high quality of milk with meager equipment, provided that careful sanitation is practiced.
The barn or cow stable should be located on ground that is well drained so that the animals do not have to wade through mud and manure in their passage through the barnyard or to the watering trough. The building should be well lighted and well ventilated, and it should have floors which can be kept sanitary.
Every farm should have a dairy or milk house. Here the milk must be brought immediately after milking for straining, cooling, and storing until it is shipped. The cooling equipment may be an insulated box built of concrete or some other impervious material, filled with cold water, and provided with a constant-level overflow pipe so that the cans can be set in the water up to their necks without any possibility of the water overflowing into the milk. Some cooling boxes are built so that a stream of cold water from a nearby spring flows constantly through them. The most dependable method is to install a milk cooler. This may be connected to a compressor operated by gasoline or electric current. In some dairies, cold-air refrigerators are installed. The equipment should be arranged so that the milk can be cooled immediately after it is strained in order that the bacterial content will not increase by incubation in the warm milk.
The dairy utensils when not in use should be kept in the milk house. They should be of sanitary construction with flooded seams (preferably welded without solder) and free from cracks, corners, and open joints where milk could accumulate and escape complete removal in the cleansing of the utensil. Partially covered milk pails have been widely recommended (and required by some health departments) to protect the milk from falling dirt. Strainers should be made without wire-mesh screens because it is difficult to clean them adequately when the milk has dried. Milking machines should be taken apart daily, and thoroughly cleansed and sterilized. All cans and utensils should be well tinned to protect them from rust, and so constructed that none of the milk can escape being removed. The best type of cans are made of a homogeneous metal (instead of tinned iron) with welded seams, and so designed that all parts of the surfaces can be seen.
Facilities should be provided for thoroughly cleansing all the utensils first in cold and then in hot water. Some farms are provided with small steam boilers for steaming thé cleansed utensils in steam chests. The utensils are then drained and stored on racks. These operations are usually conducted in the milk house.
Premises. The milking operations should be protected from contamination from pig pens, chicken yards, open toilets, drain water, and other sources inimical to sanitary milk-handling. In the absence of a flush-type or chemical toilet, a sanitary privy is required.
The water supply on a dairy farm should be potable. Extensive tests have shown that often this is not the case. Inasmuch as little can be done to remedy such a condition, food officials insist that all water for washing purposes be boiled, and they are increasingly requiring that chlorine be used in a final rinse as a factor of safety.
Methods. The milk producer must follow clean milking practices, or sooner or later his carelessness will reveal itself in the lowered quality of the milk. He should wear clean, washable, outer clothing so that he will not contaminate his hands from his soiled clothes. He should wash his hands and rinse them in a bactericidal solution immediately before milking, and dry them on a clean towel or by other sanitary means. Wet-hand milking is prohibited because the drip-pings from unclean, wet hands fall into the milk pail. The milker should not milk cows immediately after forking hay in the barn, because dust, chaff, and other such material may fall into the milk. The flanks, udders, and tail brushes of the cows should be kept clipped to facilitate the cleaning of the cows before milking, and reduce the contamination of the milk with falling hairs and dandruff. Increasingly, it is becoming the practice to wipe the udders, often with a chlorine solution, just prior to milking. In spite of great care, some particles of foreign material of one kind or another fall into the milk. In dairy parlance, this is called sediment. Many farmers remove this telltale sign of unclean and careless practices by straining the milk before delivery. Some food-control officials discourage the use of strainers in order that the dirt can be seen by the inspector and thereby direct attention to unclean production methods.
After the milk has been cleanly produced and strained, it should be cooled immediately to a temperature preferably below 50° F., but never above 60° F., and held there until the milk is shipped. This refrigeration prevents the growth of the germ life which inevitably contaminates all milk to a greater or less degree. Bacterial multiplication in the milk would sour it or otherwise spoil the flavor.
If the farmer can comply with these general requirements, his application is approved by the Health Department or the dealer's procurement department, and he is allowed to begin the shipment of milk. He then comes under the supervision of the quality-control organization of the plant to which he ships. From time to time the local official inspector visits his premises to check on the effectiveness of the inspection service of the dealer. Even where the farmers are licensed directly by the health department, regular inspection is carried on by the dealer's quality-control staff. Moreover, the state itself may have an inspection force. Sometimes two or more municipal inspection services overlap, and it is regrettable that requirements for milk production are sometimes contradictory.
Transportation. The transportation of milk to the market requires care, and the lading requires proper handling to protect it from contamination, deterioration, or spoilage. In the more backward localities, the farmer sets his cans of milk by the roadside and leaves them there for the milk hauler to pick up whenever he comes by. Usually he comes at approximately the same time each day, but there are many factors which may delay him. In the winter, the milk may spoil from freezing, and in the warm weather it may rise in temperature and become sour. If the railroad car or the truck is not refrigerated in the warm months, the milk may become warm during transit. The truck may be delayed for hours at the dairy waiting its turn to be unloaded.
To overcome these difficulties of direct shipping, there is an increasing tendency for farmers to deliver their milk by relatively short haul to a nearby receiving or cooling station. This is a small dairy plant, owned and operated by the city milk dealer, equipped with weigh scales, refrigeration machinery, and storage tanks.
Delivery. All milk is delivered either at receiving stations located in producing territory or directly at the urban pasteurizing and bottling plants. Some municipalities waive the requirement for cooling milk that is produced in the morning, provided that it is delivered at the plant within about 2 or 3 hours after milking. As the cans are unloaded onto the receiving platform, the plant inspector knocks the lids off and examines the milk for odor and appearance. Cans with abnormal milk are pushed aside for return to the farmer. Sometimes this milk is denatured by the addition of a harmless color in order to prevent the farmer from attempting to work it in with some later shipment of good milk.
The accepted milk is dumped into weigh tanks; the empty cans are immediately washed and steamed in can washers, and then de-livered directly to the farmer. As soon as the weight of the milk is recorded, a receipt is given the farmer. At this place, the sample is taken for the milkfat determination and also for the bacteriological examination. The milk is dropped into a tank, and from there pumped over a cooler to reduce its temperature below 45° F. It is then held in refrigerated tanks to await pasteurization, or is pumped directly into insulated tanks on trucks or on railroad cars for shipment to the pasteurizing plants. This transportation may require several hours, but the temperature of the milk may rise only 2 or 3 degrees, even in hot weather.
In general, the fundamental requirements for the satisfactory production and handling of milk are as follows: (a) healthy cows; (b) clean production and sanitary handling; (c) clean and sterile utensils; (d) prompt and continuous refrigeration; (e) freedom of farm from communicable disease and polluted water supply.
RELATION TO THE PUBLIC HEALTH
Composition of milk. Milk from different breeds of dairy cattle has correspondingly different composition. An extensive series of de-terminations on the whole milkings from several known breeds and crosses over their entire lactation periods are given in Table I.
In addition to breed, several other factors contribute to variability in the composition of milk. Individual cows may inherit characteristics of a richer milk production. Morning milk is usually richer than evening milk. During milking, the first portion is much lower in fat content than the last portion or strippings. Excitement of the cow may influence the composition. Seasonal changes are well-recognized factors. In general, the butterfat content is higher in the win-ter and lower in the pasture months.
Milk which is produced for a certain market may come from an area which has a cow population of some predominant breed, and, therefore, the composition of that milk may be different from that of a nearby community. However, the tendency now is to endeavor to secure a milk supply from mixed herds to produce an average composition of about 3.5 to 4.5 percent butterfat and a minimum of about 8.5 percent solids-not-fat.
Inasmuch as cream rises at a rate to form a definite cream line in an hour, it follows that any spilling of milk from a can causes a disproportionately heavy loss of butterfat. If a farmer pours the milk from one can into another or dips some milk out of the can, there is likely to be a distorted relation of percentage of fat to total solids.
All the above factors may operate singly or collectively to cause variation from day to day in the butterfat content of milk delivered by dairymen.
Standardization of milk. The demand for milk of higher butter-fat content has been increasing in recent years. The regulatory officials in some communities allow milk to be standardized in the plant to a given fat content by the direct addition (or subtraction) of cream, whereas others prohibit this practice. The same objective is attained in the plants by mixing milk of high fat content (or high test, as it is often called) with milk of low fat content (low test) in the proper proportion to yield a final mixture of the desired test. It is also attained by standardizing the milk on the farm. The three common methods used are: (a) discarding the foremilk (which is lower in butterfat than the remainder of the milk) ; (b) allowing milk to stand in cans or a tank for several hours, and then drawing off the more or less "skim" milk from the bottom; (c) skimming cream in a separator and adding it directly to the bulk of the milk; and (d) increasing the butterfat average of the herd by introducing some high-test cows or breeding the whole herd with a high-test bull. The first two methods raise the butterfat content by removing the low-test milk. The third method raises it by the direct enrichment with cream. The fourth method changes the breed character of the milking herd.
In the first three of the above practices, the normal ratio of the fat to the solids-not-fat is so altered that the milk will not coincide in its proximate analysis with any of the standard tables. Its con-tent of fat will be too high for the solids-not-fat. For example, a normal 3 percent milk has 8.33 percent solids-not-fat. If the fat con-tent is raised by adding 1 part of 30 percent cream to 26 parts of this milk, the resulting fat content will be 4 percent but the solids-not-fat content will have fallen to 8.25 percent.' This may be below the local requirements. By the lactometer (specific-gravity hydrometer for milk) the reading would indicate that the milk had been watered.
In the fourth of the above practices of fat standardization, the mixing of the breeds tends to complicate the breeding problem. The breeds will be crossed and the result will be a breed of mixed cattle with high production costs. The movement to produce pure breeds has been a profitable program for the dairy farmer because of the effect of increased qualitative and quantitative production of milk and the sale of pure-bred calves. This tendency to sell mixed milk from different breeds runs counter to this long-time program and counter-acts the development and educational work of years to produce more milk more cheaply for the benefit of producers and consumer alike.
Nutritional value. Milk is unique among foods in its nutritional value. Its proteins contain amino acids of a quality and quantity adequate for the needs of the body. Calcium and phosphorus are present in abundance and in easily assimilable form. Sherman states that, unless milk is included in the diet, it is unlikely that either the child or the adult will obtain enough calcium.
Milk is deficient in iron and copper, and accordingly it cannot be used indefinitely as the sole food for young animals.
Milk contains vitamins A, B, and G in abundance. McCollum states that milkfat is the most important source of vitamin A in the American and European diets. The content of vitamin C in milk is not large, and most of it is usually lost by the time milk is consumed. The content of vitamin D is low. Clinical experience shows that both these vitamins must be introduced into the diet from other sources.
The carbohydrate in milk is the sugar lactose. This product exercises a beneficial influence on intestinal hygiene by furnishing food for the type of microorganisms which inhibit the growth of the putrefactive and other harmful types. The galactose grouping in lactose is necessary in the formation of the galactosides of nerve and brain tissue.
The extraordinary nutritive value of milk has been demonstrated in several large-scale feeding experiments on children. In an English public school, the consumption of milk and butter was increased and that of other food decreased. Associated with these changes in the diet was an increase of about 3/4 inch in the average height of 11-year old boys and of more than 1 inch in the height of those of 15 years of age as compared with their controls. Their weight also increased, and there was a noticeable decrease in rheumatism and attendant conditions.
The effect of adding 1 pint of milk daily to what was considered a good diet in an institutional boarding-school caused, in boys 6 to 11 years of age, an increase in height of 2.63 inches and an increase in weight of 6.98 pounds, as compared with increases of only 1.84 inches and 3.85 pounds respectively in similar boys who did not receive this supplement of milk. It was also noted that, among these extra-milk children, there was less illness, especially nasopharyngeal catarrh, a reduced tendency to chilblains, a better condition of the skin, and greater alertness and high spirits. Other work along similar lines has completely demonstrated that the addition of milk to the diet of school children increases their average weight, height, strength, vitality, and general health.
Several other investigations along these lines have been reported by McCollum. He records in some detail a spectacular experiment where 84 undernourished children were divided into two groups, one fed the regular diet without milk and the other fed with one quart of whole milk each day. The milk-fed group gained consistently in weight and manifested great vitality, whereas the control group on the regular diet not only grew at a lower rate but were apathetic and more easily tractable. The withdrawal of milk from the diet of the one group and giving it to the other group reversed the picture.
The nutritive excellence of milk makes it a dietary prophylactic, as McCollum points out. He advocates the consumption of one quart per capita per day, and Sherman states that one pint must be considered as inadequate. Milk and also the leafy vegetables are the only foods that can supply the deficiencies of the cereal grains, legumes, tubers, and muscle meats, because it supplies the amino acids, vitamins, and minerals which these lack. Its protein alone is not quite the equal of the proteins of muscle, kidney, and liver, but it possesses other nutrients which taken together make it nature's "most nearly perfect food."
Organoleptic acceptance. On account of this unique food value, it is a public-health desideratum that milk take its proper place in the diet. An important item in enlightened public-health practice is to make milk appetizing and attractive. Unfortunately, milk may contain off-flavors which sometimes render it repulsive to the consumer. In fact, the number of persons who dislike the flavor of milk is very large. Factors which contribute to this condition are strongly flavored feeds, contamination of the milk with metals, especially iron and copper, bacterial growth, and lack of proper sanitation.
Dirty milk may be free from pathogenic bacteria and safe so far as communicable disease is concerned. But such milk is unappetizing and potentially dangerous, because the presence of dirt indicates carelessness in operations. An unsightly package, a dirty delivery wagon, an insanitary farm, and an unclean plant have an adverse effect on consumer appeal. Milk should be made agreeable to the palate and attractive to the eye. Quality in milk comprises safety, cleanliness, good keeping quality, a definite and reasonably constant nutritive value, and freedom from objectionable odors and flavors 13
Microbiological properties. Milk is so rich in the quality and quantity of its nutrients that it constitutes an admirable culture medium for the growth of microorganisms. It is commonly used as a differential test medium in daily bacteriological laboratory practice. Therefore, it is to be expected that, if milk becomes contaminated with infectious material, the microorganisms present will be able to multi-ply profusely, particularly if incubating temperatures prevail. It is this cultural property that makes milk a more potent factor than water as a possible agent in the spread of communicable disease. Water only carries infectious material; milk multiplies it.
When bacteria proliferate in milk, one of the constituents that is broken down is the milk sugar, lactose. The lactic acid that is formed may increase until the milk curdles. This increasing acidity has been taken as a rough measure of the germ life of a milk. Inasmuch as the number of microorganisms per milliliter increases to millions be-fore there is an appreciable increase in the measurable acidity, the test as a measure of incipient spoilage has value only when the milk is of poor quality to start with or has been handled carelessly. The interpretation of the test is complicated by reason of the great differences which exist in the acidities of different samples of pure, freshly drawn milk from healthy cows. As Sommer has shown, a milk of 0.18 percent acidity may have been produced on a farm where the best of milk sanitation and cooling were practiced, whereas a milk of 0.16 percent acidity may contain millions of microorganisms per milliliter. However, the bulk of the supply runs about 0.14 percent acidity, calculated as lactic acid.
Microorganisms in milk also attack the proteins. These are broken down into peptones and other simpler bodies, and in fact all the way to ammonium compounds. Scholberg and Wallis reported 15 that a large bacterial content in market milk caused the formation of peptones and albumoses and an unidentified transitory product which exerted a harmful effect on the pancreas. Park and Holt earlier showed that the presence of large numbers of bacteria in milk, even though these organisms had been killed by heat, caused a certain amount of digestive disturbance harmful to the well-being of the infant 16 Other investigators have endeavored to show a quantitative relation between the number of microorganisms (as determined by the plate count) and the content of ammoniacal nitrogen, somewhat analogous to the relation between the bacterial content and the amount of lactic acid present, but none of this work has progressed beyond the qualitative stage.
Sanitary significance of determinations of bacteria. When milk from healthy cows is produced and handled under well-known sanitation practices, the number of microorganisms present is relatively small and their effect on the milk is negligible. On the other hand, when the milk is produced by cows with certain diseases, or when it is produced under insanitary conditions, or when it is not adequately refrigerated, the bacterial content will probably be high. Unfortunately, careless handling does not always result in high bacterial content, nor does a high count necessarily mean that the milk is unsafe. But inasmuch as a milk of proper quality, when produced and handled in a sanitary manner, does not have a high count, it is reasonable to consider that a high count indicates that some irregularity has been practiced, particularly if inspection of the handling operations reveals improper methods or conditions.
When bacteria are counted for their sanitary significance, no at-tempt is made to differentiate them into their different groups, The count is a determination of all the different organisms which, singly or in groups, proliferate to form colonies of macroscopic size on the particular medium at the temperature in question. A slight change in the composition of the medium or the temperature of incubation will cause a greatly different count. Bacteriologists have agreed on a standardized procedure of growing the organisms on a beef-extractpeptone agar at an incubation temperature of 37° C. for 48 hours. This is called the standard plate method. It does not purport to reveal all the living microorganisms that may be present because no one medium has been found that will do this. The standard plate method is commonly used in routine control work to indicate whether or not the sample is bacteriologically normal. Although this technic is largely empiric and highly specific, practice has amply proved that it yields data of real sanitary significance. It has constituted one of the best measuring sticks that sanitarians possess for controlling the proper production of milk, and by means of it the milk industry has been brought to its present high level of sanitary excellence.
The colon group of bacteria (Escherichia-Aerobacter group, of which Escherichia coli, formerly known as Bacillus coli communis or Bacterium coli, is the best-known member) is always present in a regular milk supply. The English workers refer to them as coliform bacteria. For a long time, sanitarians believed that these organisms had the same significance in milk that they had in water, and that they indicated fecal pollution. It is true that, when milking is done under grossly insanitary conditions, the coliform count will be high. These organisms may come from human feces, or cow manure, or high-way dust, or unwashed utensils. Milk can be produced free from them, but the cost is prohibitive for the bulk milk supply. If milk is held for 24 hours at such moderate temperatures as 59° F. (15° C.), these organisms will multiply rapidly. Therefore, the number present in a given sample embraces the two factors of extent of contamination and degree of cooling. Inasmuch as there is a wide difference between the public-health significance of these two factors, and as the sanitarian in the laboratory does not know which factor was responsible for the high coliform count in the given sample, this determination has been almost entirely discarded from regular milk control for the bulk supplies which are to be pasteurized. The work of Sherman and Wing 18 shows that the coliform determination is of no special value as an index to the sanitary conditions surrounding the production of raw milk of the usual market grade. This view has very well ex-pressed the consensus of opinion of many practical milk-control officials.
Epidemiology. Public-health records bear strong evidence of the epidemiological significance of contaminated milk supplies. The incomplete list of outbreaks of disease attributed to milk presented in Table II gives some idea of the extent to which insanitary milk has been (and still is) a factor in the spread of disease.
Unfortunately, about half of the milk supply is sold in communities which have little or no milk supervision. The maintenance of the above average would seem to be due to the greater amount of effective epidemiological investigation and the increased reporting of these outbreaks.
An illustration of the extent to which milk may be an important factor in epidemiology is the spectacular and tragic Montreal outbreak of typhoid fever in which more than 5000 persons contracted typhoid fever from an infected milk supply.
Although epidemics are usually considered to be scourges on ac-count of their train of tragedy and suffering, they carry the additional onus of causing financial loss. Brooks writes [J. Milk Technol., 2, 168, (1939) ] that the New York State Department of Health investigated the economic effects of an outbreak of milk-borne scarlet fever, embracing 511 cases, on a village of 4742 population. The principal business was a shoe-manufacturing plant, employing about 600 per-sons. Reports were received from 12 stores, 2 restaurants, a garage, a chair factory, and a dentist. Their losses ranged from 10 percent up to 60 percent of their business, the aggregate financial amounts totaling $100,000. The moving picture theater closed because of falling off in patronage, but no estimate of its losses was received. In addition, the shoe company plant was badly crippled by illness among the employees, and had to shut down completely for 5 days. They estimated their losses in profits at $11,221, and the loss to workers at $38,500. This adds up to a total of $149,721, which is a fairly sizeable consideration, even if the factors of life and health were not involved. Sickness is expensive, it is an economic waste, and it is inexcusable when preventable.
Types of infection. Milk becomes infected with microorganisms from three general sources: man, cows, and environment. During milking, straining, cooling, packaging, and transporting, the milk is handled by numerous workers. If any are careless in their personal hygiene or are ill with any of the infectious diseases, such as typhoid fever, scarlet fever, diphtheria, poliomyelitis, and food poisoning, the respective germs may be introduced into the milk.
Another group of diseases may come from an infected cow. If the udder is tuberculous or the milk contains the organisms of undulant fever, these diseases may be transmitted to man through ingestion of the milk. One of the worst milk-borne diseases (on account of the high mortality) is septic sore throat, the bacteria of which may infect a cow's udder from an ill milker.
Exposure of the milk to unclean utensils, barn and road dust, and other such insanitary environmental conditions results in a collection of a miscellaneous flora of a wide variety of microorganisms which is added to the already somewhat mixed flora from the udder itself. Usually these are not pathogenic (disease-producing) but are the types that cause spoilage and off-flavors.
If the milk is kept cold, the organisms will not multiply and their effect may be negligible. However, if the milk is allowed to warm, they may proliferate to enormous numbers and produce massive doses of infection, or if non-pathogenic, may spoil the flavor and quality of the milk.
Poliomyelitis. Infantile paralysis (poliomyelitis) seems now to have been definitely added to the list of milk-borne diseases. Aycock 24 reported an outbreak which was traced to milk from a herd which was free from tuberculosis as shown by the tuberculin test and there-fore supposed to be of exceptional wholesomeness in general. The infection showed an incubation period of 6-14 days. Dingman 25 describes an outbreak which occurred at Spring Valley, N. Y., wherein 4 children who drank raw milk from a grossly insanitary dairy (called X) became definitely ill, whereas 3 other children in the same household who drank milk from another dairy did not become ill. A boy in another house who drank X's milk raw became infected, whereas the children in still another house who drank X's milk after boiling remained well. A child at X's dairy became ill on July 4, and the above cases all came down on July 18, 20, and 22. Knapp, Godfrey, and Aycock" write of an outbreak of 8 cases in Cortland, N. Y., all on one milk route, milk for which came from a farm on which there was a paralytic case. Rosenow reports 27 an outbreak in a coeducational midwestern college. He isolated the causative streptococcus from the throats and spinal fluids of cases and from the milk of healthy cows in the herd. The outbreak stopped when this milk was no longer used. The milk from a neighboring college was negative to these organisms and no cases occurred after the change in milk supply was made.
The most clear-cut evidence of all is reported by Rosenow, Rozendaal, and Thorsness in connection with an epidemic at White Bear Lake, Minn. The causative organism was found in numerous samples of the raw milk and in a few samples of alleged pasteurized milk (delivered by a dairyman who served both raw and pasteurized milk). Success in isolating the incriminated organism was due to cataphoretic studies and to the use of the special medium glucose-brain broth. The organism isolated from the raw milk at the time of the epidemic was identical with that isolated in cases of poliomyelitis in human beings and monkeys, namely: in its peculiar virulence, in its power to cause flaccid paralysis especially in rabbits, in its thermal death point, in its morphological and cultural characteristics, in its immunologic proper-ties, and in its cataphoretic velocity.
Septic sore throat. An increasing amount of evidence is accumulating that the disease known as septic sore throat is often caused by the drinking of milk which is infected with Streptococcus epidemicus from mastitis udders 29 It is believed that these cows had been previously infected by persons carrying hemolytic streptococci of the human type. There is a close relation between erysipelas, scarlet fever, and septic sore throat. The streptococci associated with these three diseases cannot be differentiated by laboratory procedures. Scarlet fever is believed to be simply septic sore throat plus the rash. Brooks considers that we are missing many milk-borne outbreaks of this infection, judging by the increasing number that are found in those states where most attention is devoted to studying the disease 31 Communities are requiring that mastitis be eliminated from the dairy herds supplying their milk.
Milk sickness. A milk-borne disease called milk sickness was formerly encountered in the central part of the country. The first symptoms are weakness and loss of appetite, followed by nausea. epigastric pain, great thirst, constipation, subnormal temperature, collapse, and often death—symptoms similar to those caused by staphylococcus toxin. Inasmuch as some persons are immune to this enterotoxin, an investigator may be misled in tracing the offending food, especially in localities where milk sickness occurs. As Couch has shown, cows develop the disease known as slows or trembles (descriptive of the animal's symptoms) when they feed on the rayless goldenrod, white snakeroot, or similar plants. The toxic principle, which is the alkaloid tremetol, passes into the milk, and poisons the animal that drinks this milk. It is now encountered only in parts of Tennessee, North Carolina, and New Mexico. No cases have ever been reported as due to the mixed milk from creameries. The disease is unknown in the cities and larger towns.
Tuberculosis. Tuberculosis in dairy cattle has been shown to be a potent source of the disease in human beings. In the United States in 1932, it was reported that 10-15 percent of the cases of bone and joint tuberculosis were of bovine origin; and that 21 percent of tuberculous children under 5 years of age, and 26 percent of those from 5 to 16 years, are infected with the bovine type. This means that in this country, about 4000 children die annually from bovine tuberculosis, and that at least 8000 cases occur.
It has generally been thought that pulmonary tuberculosis of bovine origin is rare. It is now being discovered that there are many such cases, according to reports from Denmark, Holland, England, Scotland, and Sweden. For example, out of 103 cases of pulmonary tuberculosis investigated in Scotland, 13 showed the bovine type in the sputum. In 5 of these, a history of previous glandular tuberculosis indicated that the alimentary canal was the probable channel of entry. An unusual outbreak of pulmonary tuberculosis in a Swedish rural community, affecting 50 persons, mostly children, was traced to raw milk. The herd contained some cows which were positive to the tuberculin test but were considered safe because they had no clinical signs of what was called an infectious form of tuberculosis. One cow was found to have a mastitis with the usual type of streptococcus but the milk teemed with tubercle bacilli. This cow and three others were found on post-mortem to have pulmonary tuberculosis. The striking feature of this outbreak was the apparent connection between pulmonary tuberculosis and udder infection of the cow, and the transmission of pulmonary tuberculosis to children by drinking this infected milk.
Excellent discussion of human tuberculosis of bovine origin, including the pulmonary type, is found in editorials in the American Journal of Public Health: 26, 1128 (1936) ; 27, 919 (1937) ; 28, 646 (1938) ; and 28, 1334 (1938). The U. S. Department of Agriculture, in cooperation with the states, is carrying on an increasingly effective bovine tuberculosis eradication program. At the end of 1937, the number of entire states in the modified accredited area was 44. Of all the counties in the United States, 96 percent were in the modified accredited area, and more than 99 percent were either in this area or were engaged in the area plan of testing 36 A modified accredited area is one in which the cattle which are reactors to the tuberculin test constitute no more than 0.5 percent of the total herd population. The incentive in this particular work is largely commercial on account of the emphasis on agricultural economics, but the public health receives material benefit. As soon as these prophylactic measures begin to manifest their effects, the incidence of milk-borne bovine tuberculosis may be expected to drop. Already the number of tuberculous cattle condemned to slaughter has greatly decreased. However, the discovery that generalized tuberculosis of the bovine type has been found extensively in swine indicates that foci of the bovine tubercle organ-isms still exist in territory whose dairy herds are now clean.
The possible health hazard from tuberculosis in goats is pointed out by Cunningham and Addington." They state that several goats lave been removed from the New Mexico Experiment Station herd as positive reactors to the tuberculin test, a diagnosis confirmed in most cases by post-mortem examination. The authors believe that goats kept for the production of milk for human consumption should be tested for tuberculosis the same as dairy cattle.
Undulant fever. Occasionally undulant fever (brucelliasis) is traced to dairy products. Fifty percent of many samples of unpasteurized milk marketed in Illinois have been found to contain viable organisms. The disease may be caused by the organism Brucella abortus (also known as Brucella bovis) which is the cause of infectious abortion in cattle, or by Brucella suis which causes a similar disease in swine, or by Brucella melitensis which infects goats. The last is not often encountered in this country but is known in the Mediterranean countries as Malta fever. The bovine and porcine strains have both been found to infect milk supplies, and several milk-borne epidemics have been reported. The porcine strain is probably more virulent to man than the bovine strain. Br. suis causes disease in cattle, but it is not known that Br. abortus causes disease in swine. It seems that only the occasional strain builds up a virulence sufficient to cause disease in man in view of the relative infrequency with which the disease occurs although widely prevalent in raw milk supplies.
In recent years, there has been a decided increase in the number of reported cases of undulant fever, indicating that this disease is being better diagnosed. Hasseltine points out that this disease may have an incidence rate of about one-tenth that of typhoid fever. In the past, many cases of undulant fever have been called typhoid fever, and, as the correct diagnosis of undulant fever increases, there will probably be a proportionate decrease in the recorded typhoid-fever rates by reason of this improved diagnostic development.
Staphylococci infections. As far back as 1914, Barber reported gastrointestinal illness from drinking milk infected with a white staphylococcus, but no other cases seem to have been reported until Dack and associates reported an outbreak from this organism 42 A recent one was reported by Shaughnessy and Grubb involving 25 cases, and traced to cows with white staphylococcus mastitis.
Numerous outbreaks of the common diseases such as typhoid fever, scarlet fever, diphtheria, dysentery, enteritis, and paratyphoid fever (See Table II, page 84) have been traced to infected milk supplies which had not been given adequate sanitary protection. When an unusual number of adult cases of typhoid fever, scarlet fever, and diphtheria occur within a limited period in a community, it is advisable to investigate the milk supply. A milk-borne outbreak may not be explosive in its beginning or, in fact, at any time during its course.
Definition. Milk is generally defined similarly to the definition and standard which has been adopted as a guide for the officials of the U. S. Department of Agriculture in enforcing the Food and Drugs Act, namely :
Milk. The whole, fresh lacteal secretion obtained by the complete milking of one or more healthy cows, excluding that obtained within 15 days before and 5 days after calving, or such longer period as may be necessary to render the milk practically colostrum-free. The name "milk" unqualified means cow's milk.
Cream, Sweet Cream. That portion of milk, rich in milk fat, which rises to the surface of milk on standing, or is separated from it by centrifugal force. It contains not less than 18 percent of milk fat and not more than 0.2 percent of acid-reacting substances, calculated in terms of lactic acid.
The states and municipalities also have enacted laws and regulations governing the standards for quality and composition of milk and cream. These usually set a minimum percentage content of butterfat ranging from 3.0 to 3.5, and sometimes include a total solids standard. They also set maximum limits for the bacterial content of the different kinds and grades of milk. For raw milk before pasteurization, these may range from 50,000 bacteria per milliliter to 1,500,000, and for milk that is pasteurized, 30,000 to 100,000.
Regulatory practices. Almost all the large cities in the' United States have enacted ordinances and instituted enforcement agencies to secure a milk supply of proper quality. The degree of enforcement usually scales down in most of the small communities (and some of the large ones) whose financial resources are insufficient or whose public interest has not been stimulated to provide effective enforcement machinery. Rural communities, as a rule, have only such official protection as can be accorded by the state food-control organizations, which are too inadequately staffed to give intensive and continuously effective protection to local areas.
The permit system is the common method of enforcing compliance with local milk requirements (see page 58 for discussion of the permit system).
When Rosenau, North, and their collaborators were pioneering in the introduction of improved sanitary practices in the milk industry, they became convinced that effective regulatory effort required that milk should be graded into two or more levels of sanitary quality, each with its own specifications of standards and operations. The National Commission on Milk Standards adopted three grades, designated by the letters A, B, and C, and wrote them into the milk-control ordinance for New York City in 1914. Since then, the idea has been widely used. It is called the grading system because the milk must be correctly labeled with the grade letter to indicate that it complies with the respective quality standards. If samples of a given grade are found to be below the quality of the grade claimed on the label, or if inspection of the production, processing, or delivery operations reveals violations of the respective standards, the control officer orders the labels to be changed to designate the grade to which the milk actually belongs. This is called "degrading." Inasmuch as lower-quality grades sell at lower prices, a dollars-and-cents stimulus is at once operative to induce the dairyman to use every effort to correct the cause of this action and secure the right to use the higher-grade label again.
The subject of the relative effectiveness of the single grade in comparison with the multi-grade system is still being discussed. A single grade is preferred by some officials because the time of the health officer is concentrated on substandard milk, and is not spread over the whole supply, regardless of its need for his attention. It simplifies the production and pasteurization requirements, and is equally applicable in small, medium, and large communities. The enforcement of the standards of graded milk usually requires a larger staff, and is a far more expensive operation (when really done) than the control of a single grade. The function of the health officer is to eliminate the sale of unsafe milk, which means that the poorest grade permitted in any system must be safe. This is the limit of the health officer's responsibility. The establishment and enforcement of grades is primarily a marketing problem and not a health one.
Enforcement under the grading system is considered by other milk-control officers to be easier because the principle of correct labeling is generally accepted as reasonable. A regulatory officer can more readily secure support on such a requirement than he can when he resorts to the drastic measure of excluding a producer or closing a plant because of some infraction which is practically important but difficult to defend before a non-technical board or court. De-grading is a milder weapon, and exclusion is still in reserve.
Before any drastic regulatory action is taken either to revocate a license or to degrade a supply, the licensee may be cited to appear before the control officer and make any statement of explanation, promise of correction, or any other presentation that he wishes. If this is accepted, he may be given further opportunity to show that he can operate a milk business properly, or his product may be degraded, or his permit may be revoked. Under the last contingency, the business is closed by the police.
Another method that has been found to be effective in improving the quality of milk is the procedure for rating the sanitary quality of the milk supplies of communities that have adopted the milk ordinance and code recommended by the U. S. Public Health Service. Random selection is made of farms and processing plants on the milk shed that is being rated, and each is scored on the individual farm and pasteurization plant inspection sheets. These, together with the results of examination of samples, are transferred to computation sheets where weighted averages are calculated. The ratings are measures of compliance, and are not safety ratings. They serve to indicate the weaknesses in the control procedure of the given community so that proper improvements can be made. The frequent publication of these ratings stimulates enforcement.
A device that has been helpful in improving milk quality has been the use of the score card for dairy farms. All the various items in milk production, including both equipment and methods, are listed and given numerical ratings, the relative value, of which is determined as well as can be done by technical judgment. With the card before him, the inspector marks down opposite each item the figure which he considers to represent the degree of compliance with the regulations. He then adds the list to determine the final score. Such a card is a convenient record of the sanitary condition of the dairy farm and its milk-handling operations. This reasonable use soon developed beyond the original idea of its being a convenient record, and became the basis of grading and even appraising the sanitary value of a given supply. Such an application assumed that the total score was the measure of the milk quality. Experience soon taught that no such relation existed because a given farm might rate high in some sanitary essentials (such as health of cattle and cleanliness of equipment and premises) but low in less important matters (such as distance of spring from barn or amount of window space in barn). This has led to a revision of the scoring practice whereby each item is merely checked opposite with a "yes" or "no" to indicate compliance. For discussion of the use of score cards, see Kelly and Leete, "Inspection of Milk Supplies," U. S. Department of Agriculture Circular 276, 1923.
EXAMINATION FOR UNWHOLESOMENESS AND ADULTERATION
Physical examination. Sediment. The insoluble particles of dirt can be collected on a small cotton disc and compared with standards to rate the relative degree of such contamination. The presence of mastitis curds, insoluble white curd particles, dirt, and other extraneous material as well as indications of faulty cooling can be detected by means of the strainer-dipper on the milk-receiving platforms 48
Organoleptic. Milk should look and taste natural. Any different condition warrants investigation.
Temperature. Temperatures should be taken at the farm, and also when the milk arrives at the dairy.
Chemical examination. Sampling. The collection of an authentic sample of milk requires careful attention when it is realized that a few milliliters must represent the milk in a 10-gallon can or a 2000-gallon tank. Detailed instructions are provided in Standard Methods of Milk Analysis.
Acidity. The acidity of milk is determined by titrating 10 milli-liters of milk in an equal volume of recently boiled and cooled distilled water with 0.1 N NaOH solution, using 0.5 milliliter of phenolphthalein indicator. For the interpretation of these data, see page 82.
Butterfat. In the official Roese-Gottlieb method, the milk is treated with several reagents and extracted with petroleum ether in a Rôhrig tube. The solution is drawn off and evaporated to dryness for weighing. The Babcock method treats the sample of milk with strong sulphuric acid to break the fat emulsion and to concentrate it by centrifugation in the stem of a special Babcock milk bottle where the volume of fat is read directly 4'
Added water. The presence of more than 10 percent water can usually be determined by measuring the decreased specific gravity with a lactometer, but smaller percentages are determined by an immersion refractometer or the lowering of the freezing point in a Hortvet cryoscope.
Preservatives. Formaldehyde is the only preservative that has been used in the United States to any great extent, and its determination may be combined with the Babcock test for butterfat; the formation of a violet color on addition of the commercial sulphuric acid (containing a trace of iron salts) to the milk in the test bottle is indicative of the presence of formaldehyde.
Total solids. A sample of about 5 milliliters of milk is weighed into a flat-bottom dish containing dry sand, heated to constant weight at the temperature of boiling water, cooled in a desiccator, and weighed.
Bacteriological determination. Sample treatment. Great care is necessary to secure an authentic sample, avoid contamination with other milk in the hurry of sampling on a milk-receiving platform, and prevent multiplication of the microorganisms during transportation to the laboratory.
Total bacterial counts. The most common method for determining whether a sample is bacteriologically normal is to "count" or approximate the number of colonies which grow on a nutrient agar plate incubated for 48 hours at 37° C4' For the significance of this determination, see the discussion on page 82).
Determination of colon-group bacteria. A series of fermentation tubes containing a liquid broth medium is inoculated with known dilutions of the milk, and incubated. The presence of gas in 10 percent of the volumes of the tubes constitutes a presumptive test. Confirmation is made by plating on eosin methylene blue agar, reinoculating fished typical colonies of the coliform bacteria into lactose broth, and examining under the microscope with the Gram stain.
Direct microscopic examination. This technic enables the laboratorian or milk inspector to distinguish between single cells and clumps, to differentiate between types of organisms with their attendant sanitary significance, and to observe the presence of cells and other indications of the quality of the milk 49 This Breed count, as it is often called, is made by spreading 0.01 milliliter of the sample over an area of 1 square centimeter, drying the film, defatting and staining it, and then examining numerous fields under a standardized microscope with oil-immersion lens.
Reductase test. The field of this test lies in making a rapid survey of the quality of milk where laboratory facilities are limited. One milliliter of the standard methylene blue dye solution is added to 10 milliliters of milk in a test tube. The tube is kept in the dark in a water bath at 37° C. until the color disappears. The rate of discoloration is a rough measure of the bacterial content, and conveniently classifies the milk as to its sanitary and keeping quality.
Resazurin test. The use of this dye enables the operator to classify the milk in a much shorter time than by the reductase test, and moreover, it aids in the detection of cows with diseased udders. The dye is made into a 0.05 percent solution, and 0.1 milliliter is added to 10 milliliters of milk. The blue mixture is incubated at 37° C. in a bath protected from light, and after 1 hour is compared with a standard color chart. The color changes from blue to pink according to the sanitary class to which it belongs.
Mastitis detection. Several methods are available for the detection of mastitis by the examination of the milk.
Milk from cows with mastitis can be directly examined for streptococci by plating on blood agar. The organism of bovine mastitis can be differentiated from that associated with septic sore throat epidemics by the absence of, or only weak, hemolysis, together with other cultural reactions.
The Breed direct microscopic method will reveal signs of mastitis if long-chain streptococci are found in the composite samples of the milk where at least 1 cow in 18 has streptococcie mastitis.
A mastitic condition is revealed by the use of the "strip cup." This is a metal cup with a fine screen or black cloth stretched over the mouth. When streams of an infected milk are milked through the screen, white flakes or clots will collect on the screen and be plainly visible to the naked eye.
The brom thymol blue test 52 depends on the change in color of a sample of milk to which the dye is added. One milliliter of this solution is added to 5 milliliters of the milk. Normal milk is colored greenish yellow; slightly infected milk (pH of 6.7) is colored light green; and heavily infected milk (pH of 6.9 or higher) ranges in color from green to blue, according to the intensity of the infection. This test is known commercially as the thybromol test.
The use of brom cresol purple is the basis of the Hotis test. This test consists in adding 0.5 milliliter of a sterile 0.5 percent dye solution to 9.5 milliliters of milk, and incubating at 37.5° C. for 24 hours. In normal milk the color remains purple; but if the infecting organism Streptococcus agalactiae is present, the color changes from purple to yellow.
The presence of over 500,000 leucocytes per milliliter of milk from an individual quarter, and 100,000 from a can sample indicates a possible infection.
It is generally agreed among authorities that milk from a mastitis udder will be high in its content of chlorides, but there is great diversity of opinion as to what is a normal content. This figure may vary from 0.12 to 0.18 percent. A sudden rise in the chlorine content indicates the beginning of an infection. The chlorine determination is made by adding 15 milliliters of a standard silver nitrate solution to 10 milliliters of milk, and then titrating back the excess of silver with potassium thiocyanate solution.
The above tests on samples for the detection of mastitis have not given equally satisfactory results in the hands of different investigators. Their relative reliability is critically discussed by Shaw, Hansen, and Nutting, Fay et al., and Bryan. In general, it seems that the most reliable tests are palpation of the udder, direct microscopic examination for streptococci, the blood agar plating technic, and the use of the figure of 100,000 leucocytes per milliliter to indicate the presence of an infection.
Brucella detection. The presence of Brucella organisms in milk is determined by examining the milk serum for Brucella agglutinins.
Tubercle bacilli detection. The organisms are collected from a 1-quart sample of the milk by centrifugation, and are examined by (a) direct microscopic examination for acid-fastness; (b) cultural methods on special egg medium; and (c) animal inoculation, using guinea pigs for the bovine type of tubercle bacillus, and rabbits or chickens for the avian type.
Other general types. Whenever there is evidence of the presence of large numbers of microorganisms that do not grow on the standard agar plates, special media should be used for their determination. Among these types are the thermophilic and the thermoduric types (both of which are resistant to killing by heat), and those accompanying sugar.
The inspection of dairy farms and the milk supply is usually con-ducted by a special group of regulatory officials known as dairy farm inspectors. These men visit the dairy farms to ascertain whether there is proper compliance with the regulations. Detailed inspections are made of the premises, the cows are examined and checked against the records of the veterinarians, and temperatures of the milk are taken. All utensils are examined for cleanliness. The farmer is instructed in the proper methods of handling milk, and any shortcomings in his practices are explained. Inspection is most effective when it is educational as well as regulatory.
Sample taking. There is an increasing tendency to test milk as it is received at the dairy. This gives the inspector immediate information concerning the quality of the milk. He can often show the farmer the actual test while it is being made, and secure data to guide him in making the farm inspections and in instructing the farmer in proper production methods. The usual tests that are made in this way are the sediment and strainer-dipper tests, the reductase or resazurin test, and the Breed direct microscopic test. Other samples are placed in sterile bottles, packed in ice, and sent to distant laboratories for careful bacteriological and chemical examination.
Official action. If the inspections disclose non-compliance with any of the dairy farm requirements or if the laboratory examinations show that milk of inferior quality is being shipped, the farmer is notified of such finding, and is usually given a limited although definite period in which to comply with the standards. If a re-inspection or a re-examination fails to establish correction of the difficulty, then the licensee may be summoned to show cause why his permit to ship milk should not be revoked or his milk be degraded or his supply be temporarily excluded from further shipment. In some communities, milk which has been found to be illegal is denatured by the inspector through the addition of rennet or harmless coloring matter. This automatically degrades it by rendering it fit only for use in some of the cheaper manufactured products.
The most effective control is based on a sympathetic understanding of the farmer's problems and on a conscientious effort to help him meet the proper health requirements. Conflicting regulations of different but overlapping milk sheds, arbitrary rulings of officials, and hair-splitting refinements of grades and specifications mitigate against the mutual confidence, respect, and cooperation between producer and health officer which are necessary to secure the best milk.
1. H. BuNYEA and W. T. MILLER, U. S. Dept. Agr. Farmer's Bul. 1422, rev. 1934,
2. A. E. WIGHT, ibid., 1069, rev. 1936.
3. E. LASH and W. M. MOHLER, U. S. Dept. Agr. Circular 104, 1930.
4. G. J. HUCKER, Am. J. Pub. Health, 22, 710 (1932).
5. W. T. MILLER and H. W. JOHNSON, ibid., 28, 1222 (1938).
6. W. N. PLASTRIDGE, E. O. ANDERSON, F. J. WEIRETHER, and R. E. JOHNSON, J. Dairy Sci., 19, 641 (1936); W. N. PLASTRIDGE, E. O. ANDERSON, G. C. WHITE, and L. F. RETTGER, Storrs Agr. Exp. Sta. But. 197 (1934).
7. Manual of Instructions for Veterinarians Engaged in Making Physical Examinations of Dairy Herds, N. Y. State Department of Health, Albany, Bul. M. S. 58; D. H. UDALL and S. D. JOHNSON, Cornell University Agr. Exp. Sta. But. 579, rev. 1935. 8. O. R. OVERMAN, F. P. SANMAN, and K. E. WRIGHT, Univ. Ill. Agr. Exp. Sta. Bul. 325, 1929.
9. F. C. BUTTON and E. J. PERRY, N. J. State College of Agriculture and Agr. Exp. Sta. Mint. Circ., November, 1934.
10. The Relation of Nutrition to Health. Final Report of Mixed Committee of League of Nations, Geneva, 1937.
11. E. V. McCoLLUM and N. SIMMONDS, The Newer Knowledge of Nutrition, Macmillan Co., New York, 4th ed., 1929.
12. C. L. ROADHOUSE and J. L. HENDERSON, Cal. Agr. Exp. Sta. But. 595, 1935.
13. R. S. BREED and associates, N. Y. State Agr. Exp. Sta. Bul. 438, 1917; Circular 131, 1932.
14. H. H. SOMMER, Wisconsin Agr. Exp. Sta. Research Bul. 127, 1935.
15. H. A. SCHoLRERG and R. L. McK. WALLIS, Local Government Board, Medical Officer's Rept. 1909-10, Vol. 39, p. 504.
16. W. H. PARK and L. E. HOLT, Arch. Pediat., 20, 881 (1903).
17. Standard Methods of Milk Analysis, 6th ed., Am. Pub. Health Assoc., New York, 1934.
18. J. M. SHERMAN and H. U. WING, J. Dairy Sci., 16, 165 (1933).
19. M. W. YALE and R. EGLINTON, 4th Ann. Rept. Internat. Assoc. Dairy and Milk Inspectors, p. 116, 1935.
20. C. ARMSTRONG and T'. PARRAN, JR., Pub. Health Repts. Suppl. 62, 1927.
21. Compiled from Ann. Repts. Internat. Assoc. Milk Sanitarians, and J. Milk Technol., 1 (1) 50 (1937).
22. I. A. MERCHANT, ibid., 1 (6) 26 (1938).
23. H. D. PEASE, Am. J. Pub. Health, 22, 654 (1932).
24. W. L. AYcocx, Am. J. Hygiene, 7, 791 (1927).
25. J. C. DINGMAN, N. Y. State J. Med., 16, 589 (1916).
26. A. C. KNArr, E. S. GODFREY, and W. L. AYcocK, J. Am. Med. Assoc., 87, 635 (1926).
27. E. C. RosENow, J. Infectious Diseases, 50, 377 (1932).
28. E. C. RosENow, H. M. ROZENDAAL, and E. T. THORSNESS, J. Pediatrics, 2, 568 (1933).
29. C. L. SCAMMON, Am. J. Pub. Health, 19, 1339 (1929) ; P. B. BROOKS and W. D. TIEDEMAN, ibid., 27, 334 (1937).
30. I. A. MERCHANT, J. Milk Technol., 1, (6) 26 (1938).
31. P. B. BRooxs, Am. J. Pub. Health, 19, 1009 (1929) ; 23, 1165 (1933).
32. C. S. BRYAN, J. Milk Technol., 2 (1) 32 (1939). 142 (1934).
33. J. F. CoucH, U. S. Dept. Agr. Circular 306, 1933.
34. Editorial, Am. J. Pub. Health, 22, 840 (1932) ; 24,
35. Editorial, ibid., 27, 919 (1937).
36. Report of the Chief of the Bureau of Animal Industry, U. S. Dept. Agr., 1937.
37. O. C. CUNNINGHAM and L. H. ADDINGTON, J. Dairy Sci., 19, 435 (1936).
38. C. P. BEATTIE and R. M. RICE, J. Am Med. Assoc., 102, 1670 (1934); G. E. ATWOOD and H. E. HASSELTINE, Pub Health Repts., 45, 1343 (1930) ; M. H. CAMPBELL, Vermont Agr. Exp. Sta. But. 382, 1934.
39. R. GRAHAM and J. P. TORREY, J. Am. Vet. Med. Assoc., 88, 614 (1936), from Nutrition Abs., 6, 482 (1936-7).
40. R. R. BIRCH, 23rd Ann. Rept. Internat. Assoc. Dairy and Milk Inspectors, 1934.
41. H. E. HASSELTINE, Am. J. Pub. Health, 21, 519 (1931).
42. G. M. DACK, ibid., 27, 440 (1937).
43. H. J. SHAUGHNESSY and T. C. GRUBB, J. Infectious Diseases, 58, 318 (1936).
44. "Definitions and Standards for Food Products for Use in Enforcing the Food and Drugs Act," S. R. A. Food and Drug 2, fifth revision, November, 1936.
45. G. A. WEST, 22nd Ann. Rept. Internat. Assoc. Dairy Milk Inspectors, 1933, p. 238; L. C. FRANK, ibid., p. 245.
46. L. C. FRANK, A. W. FUCHS, and W. N. DASHIELL, Pub. Health Repts., 53, 1386 (1938).
47. Standard Methods of Milk Analysis, 6th ed., 1934, Am. Pub. Health Assoc., New York.
(a) Sediment, p. 44.
(b) Sampling for chemical determinations, p. 76.
(c) Acidity determination, p. 77.
(d) Fat determination: Roese-Gottlieb, p. 81.
(e) Fat determination: Babcock, p. 82.
(f) Added water, immersion refractometer method, p. 85.
(g) Added water, cryoscopic method, p. 86.
(h) Total solids, p. 77.
(i) Sampling for bacteriological determinations, p. 12.
(j) Total bacterial counts, p. 19.
(k) Presumptive test for E. coli, p. 49.
(1) Breed direct microscopic count, p. 28.
(m) Reductase method, p. 38.
(n) Hemolytic streptococci, p. 63.
(o) Mastitis streptococci by direct detection, p. 36.
(p) Other types, p. 60.
48. J. F. JANSEN, 9th Ann. Rept. N. Y. State Assoc. Dairy and Milk Inspectors, 1935, p. 93.
49. R. S. BREED, N. Y. State Agr. Exp. Sta. Bul. 566, 1929; 568, 1929; C. S. BRYAN, et al., J. Milk Technol., 1 (5) 26 (1938).
50. G. A. RAMSDELL, W. T. JOHNSON, JR., and F. R. EVANS, J. Dairy Sci., 18, 705 (1935) ; W. D. BARRETT, H. RUTAN, and J. A. KEENAN, ibid., 20, 705 (1937); J. Milk Technol., 1 (1) 22 (1937).
51. H. MOAK, Cornell Vet., 6, 36 (1916).
52. G. J. HUCKER, N. Y. State Agr. Exp. Sta. Bul. 626, 1933.
53. H. P. Hans and W. T. MILLER, U. S. Dept. Agr. Circular 400, 1936.
54. G. J. HUCKER, 10th Ann. Rept. N. Y. State Assoc. Dairy and Milk Inspectors, 213, 1936.
55. G. P. SANDERS, J. Dairy Sci., 21, 153 (1938).
56. A. O. SHAW and associates, ibid., 20, 199 (1937).
57. A. C. FAY and associates, ibid., 20, 442 (1937); J. Milk Technol., 1 (4) 38 (1938).
58. I. F. HUDDLESON, Am. Pub. Health Assoc. Yearbook, 1934-5, p. 130; 1936-6, p. 118.
59. W. A. HAGAN, ibid., 1934-5, p. 126.
60. W. D. TIEDEMAN, J. Milk Technol., 1 (5) 17 (1938).
Associates of Rogers. Fundamentals of Dairy Science, 2d ed., Reinhold Publishing Corp., New York, 1935.
W. L. DAVIES, The Chemistry of Milk, 2d ed., Chapman and Hall, Ltd., London, 1939.
H. H. SOMMER, Market Milk and Related Products, The Author, Madison, Wis., 1939.