The Unicellular Micro-Organisms

( Originally Published 1909 )

AFTER the discussion in the previous chapter of the subjects of Reproduction and Heredity, we now can properly allude to the subject of Abiogenesis, which means either the spontaneous or artificial generation of life from nonliving sources. Some experimenters have seemed to think that by bringing together in proper conditions the physical components of living things and subjecting them to the action of various forces, life might be generated anew much as spontaneous combustion sometimes occurs in collections of inflammable materials. This apparently not improbable surmise has led to speculations about abiogenesis from ancient times, because a priori there seemed to be no logical reason for denying that as physical life must have had a beginning once on this earth, this might happen again. This conclusion is all the more natural for those who maintain the doctrine of the physico-chemical origin of life, because all the physical and chemical elements are yet with us as effective as ever. Repeated attempts, there-fore, have been made to produce life artificially, and occasionally we hear of such experiments being apparently successful. But to be living, such an artificial specimen must be capable of a cell formation which then goes on to reproduce itself by cell division or mitosis, and then continues to do so independently for successive generations. If it can do nothing of the kind, then this supposed living substance is a delusion.

But it would seem as if this subject could be best investigated in that great division of the living kingdom which is composed wholly of unicellular organisms, or living things which have but one cell to their physical being. This apparently would make our problem quite simple, for as there are no complex relations with other things to interfere, we have but one living thing before us which lives, reproduces itself, and dies the same small, single, unicellular entity throughout. Moreover, these things are universally rated as the lowest and simplest forms of life and therefore possibly not far removed from the inorganic kingdom.

But the more we learn about the unicellular world of life, the more unthinkable abiogenesis becomes.

In the first place, unicellular forms differ widely, and yet so definitely between themselves that they can be divided into four distinct genera. First come the Protozoa, which are of animal nature. Second, the Bacteria, which have vegetable affinities. Third, the unicellular Algae, and fourth, the Foraminifera.

Among bacteria there is no mixture or crossing to anything like the degree to be found among visible plants and animals, but each species has its own specific characters, making it as unlike other bacteria as any two living things can be, for example, a horse and a camel. A typhoid bacillus can by no possibility become an influenza bacillus, nor that in turn a leprosy bacillus. Each species presents a multitude of its own distinguishing features, as the following facts demonstrate.

Thus, though it may seem odd to speak of size as a feature among microscopic living things, yet they actually do vary in this respect as much as visible forms do. The bacillus of anthrax is as much larger than an influenza bacillus as a cat is larger than a mouse. But the influenza organism is a magnate compared with the yellow fever agent, for this is so small that not one of our wonderful microscopes has yet caught sight of it, and that this is due to its al-most inconceivable minuteness is shown by its passing readily through the pores of a Berkeley porcelain filter which stop the larger bodied organisms of smallpox.

But the difference in size is a minor mat-ter compared with the great contrasts in vital properties between the various species of these unicellular forms. A tubercle bacillus is in every respect wholly unlike the bacillus of the bubonic plague. The first generally takes months or years before it completes its work, while the other is never chronic, but runs its course in a few days. They differ as much also in their chemical composition and in the chemical accompaniments of their growth on non-living media. Again, some bacilli are non-motile, or can scarcely be said to move at all, but the cholera vibrio squirms so incessantly that no snapshot of it can be taken, all its micro-photographs being blurred because it will not keep still. Meantime, each of these agents kills its victims in wholly dissimilar ways. Some of them will attack the same person only once, while others find a previous attack makes another all the easier. And so we might go on enumerating many other absolute and fixed characteristics which distinguish these unicellular forms of life from one another, but enough has already been adduced to establish the fact that no forms of life anywhere are so individual and specific in their kinds as the unicellular forms.

In this respect they markedly differ from all other plants and animals. In the unicellular forms but few and relatively incomplete variations occur, such as between the avian, the bovine, and the human varieties of tubercle bacilli. But these are so little removed from one another that their title to distinct species is still doubtful. The same may be said of the colon group, to which the typhoid bacillus belongs. More can be said of the changes in the variola agent in vaccinia by change in its soil or medium of growth. When changes are artificially produced in them by altering the medium or soil in which they grow, no new species is thus formed, for they either die out or revert to their original characters so soon as their original native conditions are restored. Hence, no permanent and general modification takes place in them, as in visible plant forms like the botanical family of the solanaceae, for example, which includes such divers forms as the potato, the eggplant, the thorn apple or stinkweed growing about our barn-yards, the hyoscyamus, and the belladonna or deadly nightshade vine. That excellent botanist, however, the potato bug, if potato vines give out, at once turns to what eggplants he can find, and those failing, he eats the stinkweed, and lastly the belladonna vines.

But as to unchangeableness we may say that empires have risen and fallen, great races of man have come and gone, yet the tubercle bacillus causes in us the same tuberculosis which Hippocrates so well described, two thousand three hundred years ago, and some think that Ebers' Egyptian papyrus alludes to tuberculous ulcers thirteen hundred years before Hippocrates. Had Hippocrates only possessed a properly equipped laboratory he might then have identified the tubercle bacillus and distinguished it from other bacilli, because it takes a characteristic stain with methylene blue made faintly alkaline with caustic potash, and it contains more fat than any other bacillus. . . . Likewise the bacillus of leprosy has come down the same through the ages, from the early dynasties of Egypt, and in the Book of Leviticus it is wisely ordered to burn the plaster of a leper's house. In the sixth chapter of First Samuel, a severe epidemic is narrated as having occurred among the Philistines, which must have been the bubonic plague, for the Philistines are said to have made, in order to appease their gods, golden images of buboes and of rats ; for the term mice, in the English version, represents a Hebrew word which included both mice and rats. It was not till more than three thousand years had passed that the Japanese bacteriologist, Kitasato, demonstrated that the plague is conveyed to human beings by fleas which have bitten rats sick with the plague. Smallpox was described by Chinese physicians more than a thousand years ago, and this infection continues its same nefarious ways till now. Yellow fever remains the same yellow fever in every respect as the first historic description given of it.

This mention of smallpox and yellow fever justifies our alluding to the contrasts between the living agents of these two infections, if only further to emphasize the specific differences which distinguish them from one another. The yellow fever germ can go nowhere except as his mosquito nurse carries him. Moreover, he cannot endure the slightest touch of frost, though that may not be fatal to his mosquito. He has never been known to ascend mountains. The smallpox agent, on the other hand, can be carried by anything, as was illustrated on one occasion by an official visit of mine to a smallpox hospital, accompanied by a confrère. There was but one smallpox patient in the building, and we were careful not to come near enough to touch him. We then proceeded directly to the steamboat waiting for us on the East River, which at that time was filled with floes of ice, and we paced the deck in a biting cold wind, hoping thereby to disinfect our clothes. After a two miles' trip we landed, when my colleague took his carriage to visit a woman whom he had attended a few days before, in confinement, with a pair of twins. Twelve days afterwards both infants broke out with smallpox, to the consternation of the mother, and the feigned astonishment of my colleague.

We may remark in passing that the infinitesimal size of the agent of yellow fever raises the question how much of that substance called matter is necessary to make a powerful living thing. It is hard to imagine anything more effective than it in the work it does, which may destroy in a few hours a strong man in the prime of life, not because it is a chemical poison, but because it is a living growth belonging to an infection historically known for centuries. We cannot expect therefore that experimenters will soon be able artificially to make life, when not only the yellow fever agent, but those of hydrophobia, rinderpest, and a number of other infections of cattle, are not large enough to be seen by any microscope, and hence are beyond handling.

We have shown in the previous chapter that Reproduction and Heredity are the two fundamental factors in all physical life, and how impossible it is to find any analogue to them outside the domain of life. But much the most striking illustrations of both great reproductive powers and of heredity are shown, for example, in the case of the tubercle bacillus. His term of life, instead of being, as with us, three-score years and ten, is only from twenty to thirty minutes, but he can have 17,000,-000 descendants in twenty-four hours. Now, estimating the life only of an elderly tubercle bacillus at thirty minutes, and then calculating how many generations he goes through in the three thousand years since we have made his acquaintance, he has traced his descent through 5,450,000 generations, without once deviating from the venerable type with which he began. This only illustrates afresh what a complex and absolutely unique thing life is. When lately a new star suddenly flashed in the heavens and after a time faded away, astronomers agreed that the origin of this latest " Nova " was from the collision of separate stars or of streams of meteorites, which, judging by the rate at which light travels, probably took place while Solomon's Temple was in building. But the problem of the origin of a star is simple enough compared with that of one bacterium.

A fact which overshadows all others about unicellular forms was naturally not suspected until after microscopes were made. But it is now revealed that this once invisible world is much the largest division of the living kingdom, exceeding in actual bulk all visible plants and animals put together. To illustrate their relative extent we might liken the unicellular kingdom of life to a lake, that of all visible plants to a pond, and that of all animals to a pool. This is because all visible plants and animals are necessarily local even a tiny blade of grass is not found everywhere while among the unicellular forms the bacteria alone may be said to be every-where, on everything and in everything, whether in earth, water, or air. Nor, as we shall see, are they there in vain. Sim-ply to illustrate this vitally important fact, we may dwell on the scene at a surgeon's operating table in one of our mod-ern hospitals.

The surgeon himself and all his staff are dressed like the old priests of Solomon's Temple, wearing white caps and gowns, with the nurses standing around like priestesses all in spotless white, while every one about the table has gone through as many ablutions as befits the occasion of a bloody sacrifice under the auspices of the immaculate Goddess of Cleanliness. A minute and elaborate ritual has been observed of sterilizing everything towels, threads, needles, forceps, instruments, and what not, while the floor itself is made of glass or glazed tiles, rather than of wood. The surgeon himself does not venture to cut the victim till he has put on his sterilized gloves, because he cannot possibly clean his own fingers enough. Should any onlooker take his hand out of his pocket to reach for the gaping wound he would be ejected instanter for spoiling the whole performance with his defiling touch.

Every item and detail in the foregoing description simply illustrates how nothing escapes being covered with these unicellular micro-organisms.

But instead of associating bacteria, as many do, with nothing but surgery or disease, we cannot but infer that such a preponderating realm of life as that of the micro-organisms must have a corresponding influence on the rest of the living king-dom. And so indeed it has, because, were it not for the bacteria alone, all visible plants or animals would soon cease to exist. Thus no animal or plant spontaneously decomposes after it dies, any more than do stones or rocks. Every tree which falls in a forest and the body of every beast dead in the field, would stay there but for bacteria. So soon as any living thing gives up its life, bacteria immediately set to work upon its remains and forth-with resolve them into their original chemical elements. We can prevent all this by means which keep bacteria quiet, as when we preserve meats and vegetables with certain varieties of carbolic acid called spices, for all spices can be made artificially out of coal tar. Or we may use nature's efficient germicide, ice. Thus Nature has a great cold-storage plant in the tundras of Siberia, where the carcasses of big mammoths have lain for unnumbered centuries with their bodies so well preserved that dogs at once help themselves to them when they are dug out, and what the dogs leave the bacteria at once dispose of.

Geologists tell us that, as it is, entire strata of rocks on the earth's surface are largely made up of the skeletons of once living forms. Hence if it were not for bacteria, corpses would soon pile higher than the Andes, and the earth would be choked with its own dead. In other words, bacteria keep life going by removing the bodies of each generation to make room for the next. Thus life here begins with microbes and ends with them. In this sense, therefore, bacteria are indispensable. We could not do without their post-mortem activities.

On the other hand, certain kinds of bacteria can be made directly beneficial to the living human world by materially in-creasing its food supply. Though no one would think of cultivating protozoa, yet these particular bacteria being vegetables we can raise profitable crops of them, so that some are now actually put out for sale at two dollars a small bottle.

These valuable bacteria were first discovered in little excrescences resembling warts on the rootlets of leguminous plants such as beans, peas, and clover, and were first mistaken as signs of the plants being diseased. Further investigation proved that they were caused by colonies of bacteria which had the invaluable property of what is termed " fixing " the free nitrogen of the air. Nitrogen is a most important ingredient in all real foods, whether meat or bread, but though three-fifths of the air is composed of nitrogen, none of this vast supply can be used for food any more than the water of oceans can be used for drink. Cereals like wheat can get the nitrogen for their seeds only in the small quantity and roundabout ways afforded by decomposing animal secretions or other decaying organic matter. Hence the high price of manure per load.

Meantime bread-eaters are increasing at such a rate that according to Sir William Crookes, much too soon for comfort, there will not be manure enough, nor any other supply of available nitrogen to feed the nations. The store of Chili saltpetre, which was originally a vast deposit of guano, is being reduced at a disquieting rate, and the plan of fixing air nitrogen by electricity, though promising, is still ex-pensive. It is therefore welcome news to hear that these benevolent hordes of bacteria have been discovered in the very act of " fixing " nitrogen, and moreover just where it is most wanted, viz., on the root-lets of plants. Professor Hilgard of the University of California, in his treatise on Soils, p. 155, says that seeds sown after they have been inoculated with the purchased bacteria at the cost of two dollars an acre, can add thirty to forty dollars' worth of nitrogen more and better than the nitrogen in two tons of a chemical fertilizer such as the Chili saltpetre.

Professor Whitney of the United States Department of Agriculture goes so far as to say that it makes but little difference what the soil is, for bacteria of the proper sort will make it fertile, and that the future of agriculture will be bound up in the application of the science of bacteriology. This science is yet in its infancy, and it is now difficult to gauge the extent of its possible advantageous developments. But already we know that trees need bacteria to prepare their food for them, and that America will be as treeless as Greece and Palestine now are, if we do not put a stop to the washing away of the bacteria-laden soil by the wholesale cutting off of our forests.

The Protozoa are, if anything, of more ancient and unvarying lineage than the bacteria. So far as we are concerned, those of them which cause disease are more to be dreaded than disease-producing bacteria. Their chief mode of entrance into the bodies of animals is by the bites of insects. Thus the organism of ague or malarial fever, and the yellow fever thing, come through hypodermic injection into us by two separate varieties of mosquitoes. None of the one hundred and twenty-three remaining varieties of mosquitoes do more than sing and sting. The terribly mortal disease of Eastern India, called Kala azar, which destroys ninety-eight per cent. of those attacked, comes by the bites of bed-bugs. But a special interest attaches to the fatal Sleeping Sickness of Africa, as that is due to the bite of the tsetze fly, which harbors in its mouth species of protozoa called trympanosomes. This tsetze fly is responsible not only for fearful human epidemics but for the destruction of vast numbers of cattle, and also for the deaths of some of the largest forms of wild game in Africa. It is not improbable that many of the earth's large animals now extinct may have been killed off by similar means, for Professor A. D. Cockerell of the University of Colorado has found fossil tsetze flies in the Miocene strata of Colorado, and Professor H. F. Osborn of Columbia University has made a similar discovery in the tertiary strata of the same region. And so we will find the evidence accumulating that " the everlasting hills " themselves will not last nor be as abiding or unchangeable as are many unicellular forms of life.

This unchangeableness of certain forms of life through unimaginable antiquity is impressively illustrated by those unicellular algae called Diatoms, whose survival may be largely due to the indestructible case of flint which each individual of them forms about itself. Here we find that inscrutable, sticky thing called protoplasm fashioning coverings for itself of the most varied and exquisite patterns in Nature made out of pure silex, some in spheres, others in squares, others in triangles, others in spindles or veritable microscopic canoes, many of them with most beautiful colors, and all with delicate lines coursing over them. As the powers of great telescopes have been rated according to their resolving certain nebulae into distinct stars, so the powers of microscopes have been judged according to their ability to re-solve the lines on certain diatoms into linear dots, as in a copperplate engraving. But whole strata of rocks have been found in different parts of the world made up chiefly of the skeletons of diatoms. One such near Richmond, Virginia, is of much commercial importance for making polishing powders, and is even used in the manufacture of dynamite. But I have found in the sediment of a pool in our Central Park a number of the same species of diatoms which are taken out of rocks of the Cretaceous Period! And these living things are still at their proper business the world over, for the bases of the high walls of ice which the sea washes around the great Antarctic continent are brown with them.

But for pure antiquity and unmitigated conservatism in keeping to old ways, those living things called Foraminifera take the palm. But for them geology would be only a physical science, such as a professor of it would find now on the dry, lifeless Moon. The foraminifera, instead of choosing flint to clothe themselves withal, have taken for that purpose the carbonate of lime which abounds in sea water, with the result that a great part of the crust of the globe has been constructed by them in the form of massive strata of lime-stone, chalk cliffs and deposits, great both in thickness and in extent. It is doubtful indeed if there be any limestone which does not owe its origin to these organisms, because marbles which show no traces of them prove on examination to have been subjected to far fiercer heat than that which would consume the remains of organisms in kiln-baked brick. This heat may have been engendered in many cases by the violent crumpling up of rocky strata during great movements of the earth crust, thus changing the original limestone deposits into veins of marble.

But elsewhere limestone proves on examination to be a very curious thing, full of minute holes which are really where little canals have been cut across, and which canals cannot possibly be of mechanical origin, for no mineral grains can be made to take such lines. Instead it is now demonstrated that it is all done by an animal organism which, when first identified, was imagined to fulfil all the conditions for a beginning of unorganized life, and therefore was called sarcode. A particle of this jelly-like sarcode is observed in living foraminifera to throw out long threads which, however, are soon delicately encased by carbonate of lime, and as this shell remains after the animal which made it dies, so it stays as a slender tube of stone, thus explaining both the canals and the holes through which the sarcode threads exude, and from whence the name foraminefera. It has been demonstrated, however, by Oscar Hertwig and by other competent observers that this apparently simple sarcode contains that great official, the Nucleus, with all his high prerogatives, to whose agency must be attributed the remarkable constructive powers of these organisms. Some of their kinds live in fresh water where they, however, have no lime to work with, but their protoplasm is equal to the occasion, for they then make an envelope of Chitin, a substance which is the animal analogue of vegetable cellulose.

Foraminifera therefore are virtually unicellular, though with the important difference that they have no cell wall. Instead their protruded threads of protoplasm wherever they meet start a new organism of their kind and thus may make a collection of relatively great size.

We reproduce a plate here from Dr. W. B. Carpenter's article in the Encyclopaedia Britannica on the Foraminifera, of the forms produced by them as they are found in limestones, which shows at a glance that they can no more be accident-ally thrown together thus than a piece of printed newspaper can spontaneously come into existence anywhere. The bit of newspaper may tell something about the earthquake of Messina, but the limestone inscription by the foramimfera may as plainly tell a story of the doings of life and of nothing but life, some forty million years ago.

One needs, however, first to take some exercises in thought expansion before this story can be fully appreciated. Limestone strata, as we have said, make up a great part of the crust of the globe. But when we study how the strata succeeded one another in time, we become staggered with the signs of the presence of the Eocene Canadense in the limestone underlying the Laurentian rocks. Whole mountain ranges then towered above the sea and sank again; sea became land and land sea; climates changed from warm to cold and back again; environment changed and changed, and yet these foraminifera are still at their ancient doings the same as ever, so that if the present ocean bed were raised as in former times, new chalk cliffs would appear as of old. As Dr. Carpenter says, these foraminifera as long ante-dated the first fossils of multicellular form in the Lower Cambrian as these last antedate us. Therefore untold mil-lions of years of active unicellular life passed before the time carne for a single multicellular organism to come into being.

Having reviewed some of the aspects of the unicellular forms of the living kingdom, it is now time to consider their relations to our subject of the origin and nature of physical life. We may ask:

I. What is the answer to the question, How did life begin on this globe, and in what form or forms? The answer is that it did not begin in an accidentally formed jelly, for such an event never happened in millions upon millions of years and hence cannot happen now, for not a single bacillus, nor protozoon, nor diatom, nor any foraminifera can now be made by anybody.

II. This primeval living matter when it came into existence did not forthwith be-gin to vary in all directions, because these old unicellular things vary the least of anything on earth. Mountains may change, but not diatoms nor protozoa.

III. They were neither created nor modified by their environment, because all conceivable changes of environment have passed over them in their long story with-out ever having made them at all different from what they are now. Some of their species died out, perhaps of pure age, but not from destructive environment, because those forms which still exist are neither their survivors nor successors, but can be found to have been living and multiplying and acting through all the past ages.

How, therefore, is all this greatest story of physical life to be accounted for? The answer is one which will have to be repeated more than once as we proceed, namely, that we do not know, nor apparently does anybody else know. It is only uninstructed impatience which will assert that more than a tithe of the laws of life have been as yet thoroughly discovered and known.

Because it was not from lack of susceptibility on the part of unicellular organisms to every alleged influence of environment that their unchangeableness was due, for their living forms now show as much sensitiveness to such influences as do other living forms, and hence presumably they always have done so. Among bacteria, for example, a severe struggle is always going on between different kinds for possession of the field. One of the greatest difficulties of the bacteriologist, when he tries to isolate any one form on his culture medium, is to prevent it from being invaded by other bacteria which exterminate his chosen kind. It is the word, contamination, which vexes this scientific experimenter's soul, more than that of any gardener when he sees weeds multiplying in his carefully tended beds. Like-wise our great disinfectants, fresh air, sun-light, and washing, all act by destroying or weakening bacteria by causing changes in their environment unfavorable to their growth. Even the foraminifera find the Arctic seas too cold for them. ,But not-withstanding all this susceptibility to environment they hold on. The tubercle bacillus, though only seven minutes' exposure to sunlight kills him, yet has remained the same bacillus for thousands of years, nor once shown a fancy to become an anthrax bacillus nor a cholera vibrio, nor anything else but a tubercle bacillus. It must be some unknown power or principle of life which first gave origin to these living things and by which they remain the same to-day, yesterday, and for the future. This power or principle of life we can now only designate by the letter X, and many more such Xs we are yet to encounter.

Meantime, this great division of the living kingdom still exists as great as ever, and proportionately great in its influence upon the life of all present and more re-cent living things, ourselves included. In our next chapter we shall see that we live here only on temporary sufferance by the unicellular things, which sooner or later will put an end to our earthly existence. This subject, therefore, becomes a very practical one for us, multicellular beings, as all our Health Officials will testify.

On the other hand, we cannot but consider it strange that this greatest of the divisions of the living kingdom is wholly ignored by writers on biology. Darwin himself never once referred to it, though as his great work had for its title the Origin of Species, he would have found better examples of settled and definite species among the bacteria alone than he would have found anywhere else. This omission of the first and longest chapter in the history of life on earth is parallel to Victor Hugo's views on the people, institutions, and laws of Great Britain based upon his observations of the inhabitants of the Channel Islands, Jersey, and Guernsey, because they spoke French!

Considering what the principles of history are, this usual beginning by biologists of the story of life on earth with the late appearance of the multicellular forms, is like a philosophical history of the great American Civil War opening with the year 1861, without a single reference to any of those antecedents which profoundly influenced both the inception and the course of that conflict.

But the mention of the tubercle bacillus alone suffices to illustrate the importance of the relation of this great kingdom of unicellular life to us. For ages upon ages this mighty micro-organism has waged a cruel, destructive war upon the human race. After fifty years of observation and study of its ghastly doings, I can say that I would rather have the power to cause the tears shed on its account to cease than to be the greatest official or the greatest owner on the earth. Meantime its absolutely specific properties, which remain unchanged through the centuries, show that a physico-chemical explanation of the origin of this ancient foe can be expected only by uninstructed intellects.