Popular Science Monthly/Volume 47/May 1895/Microbes as Factors in the Society

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IN an address delivered before the Anthropological Society of Paris, July 2, 1867, Paul Broca very neatly emphasized the fact that the population of a country can not increase indefinitely. As the population multiplies on a territory that is extensible, the more undesirable lands are gradually improved and occupied. The holdings are made smaller, woods are cleared, barren tracts are fertilized, and marshes are drained. Till these works are completed all goes well, but the time comes at last when every place is occupied. The resource remains of emigration to unsettled countries. Our planet, however, is not elastic; when all of it is occupied and bears all the population it can sustain, what will then become of the human race? The balance of population and resources is kept up by death, which cuts down the living and leaves the places they filled to the newborn.

Dead beings, too, must be got out of the way. Even in that condition they claim too much space. They, moreover, fix an important quantity of matter—that of which their tissues are constituted. Matter, we all know, is not infinite in amount; it is undergoing incessant transformations, and is never created. It is therefore necessary that dead organic matter, which is essentially insoluble, be disaggregated, dissociated, and dissolved, to be fixed again by new beings. This is accomplished through the intervention of the phenomenon of decomposition or putrefaction. Putrefaction, Pasteur has demonstrated, is the function of microbes. Without them the disaggregation of matter which would probably be produced by solar radiations would be absolutely insufficient; consequently matter would accumulate in continually multiplying and insufficiently dissociated organic combinations. Without microbes, therefore, life would not be able, for lack of available matter, to continue on the globe. Applying these data to the accumulations of human beings which make up societies, we find that they are rigorously exact. We have, then, in this reduction of fixed matter to conditions under which it can be assimilated, the first and a considerable function which microbes perform in society.

Microbes have other equally important and useful offices. Of these is their action in digestion. Ordinary digestion is performed in the stomach and the intestine by means of soluble ferments secreted by the organic cells, which attack alimentary substances, dissociate them, and render them assimilable; and this is perceived to be a function very similar to that of microbes. The digestive passages, however, contain immense quantities of microbes continually brought in with the food, multiplying infinitely, and performing exceedingly complex offices. Even if we take up only a few of these offices, we are compelled of necessity to assume that they intervene in digestive operations, either as aids to the organic diastases or as themselves effective agents. M. Duclaux, insisting on this point, has remarked that some celluloses are capable of being attacked only by microbes, no organic juice having sufficient strength to affect them. M. Pasteur does not believe in the possibility of digestion in a medium completely deprived of microbes.

Of the chemical activity of microbes, what we know is as nothing in comparison with what it may be. Every species, every race, every variety of microbe is charged with a special function; the division of labor is carried among them to its extreme limits, so much so that in any chemical reaction each microbe takes its part in producing the process at different stages. Each variety has its duty in the work, determines a partial dissociation of the material which another species completes, and so on to the extreme simplification of organic matter, reduced to its elementary constituents, or to such conditions as to be assimilable by the plant.

These chemical actions determined by the microbe are therefore infinite and infinitely varied. Take two examples among a thousand. Starting with a single body—sugar, for example—the microbes may transform it into dextrolactic or serolactic acid or an indifferent acid, according to their own activity, the culture medium, or the associated reactions. Reducing agents in a high degree, microbes transform sulphates into sulphites, and even into sulphurets, the latter yielding, still by means of microbic reactions, sulphohydric acid. Thus, by this mechanism of successive dislocations, microbes, starting from sulphates, end by producing sulphurous water. This simple enunciation of a very special microbic process illustrates the extreme complexity of the chemical function of microbes, which are furthermore often aided in their work by solar radiation, likewise a powerful chemical agent, the action of which, though less immense than that of microbes, is similar to it. As a chemist, the sun proceeds like a microbe—a strange and remarkable similarity of action, mentioned by Claude Bernard in his last notes, and now demonstrated by M. Duclaux and his pupils. The climax of these complex chemical reactions is reached in the humus, which is compared by M. Duclaux to a laboratory in ceaseless activity, into which the primary matter is continuously entering to be worked up there and transformed into new products assimilable by the plant.

Availing itself of the action of an external force, the solar light and heat, this laboratory employs as its workmen the microbes, which only are capable of carrying the complicated task to a good result. Fixers of nitrogen, for example, in the nodular formations of the leguminous plants, preparers of nitrates, and constantly producing soluble organic substances at the expense of insoluble matters, the microbes work untiringly in this vast abode of chemical transformations.

Yet more: as old as the living world, contemporaries of the earliest generations of plants, microbes have contributed in a powerful way to the constitution and formation of the geological strata. Peat, which later becomes coal, has been formed by the action of microbes; they have been the agents in the complex processes of precipitation by which the immense masses of various limestones have been formed; they have played a part in other reactions from which deposits of iron, sulphur, and most of the metals have resulted. This enumeration might be very much extended. These innumerable and strong chemical actions, ancient as some of them are, still play an immense part, which is absolutely necessary to the existence of the social medium. From the point of view solely of producer of coal and preparer of iron, the microbe justifies its claim to be an agent indispensable to the life of all society. But its function is still more complex and extended.

The chemical work of microbes is often used industrially by man. Two examples in which this is done may be taken as typical. Indigo is extracted from a plant which is cultivated chiefly in India, Japan, and Central America. The plant contains a sugar, indiglucin, which is separated by washing in warm water, and is then subjected to a special fermentation. The microbe splits it into indigotin and glucose. The indigotin, which is colorless, is oxidized, still by means of a microbial! reaction, and is transformed into blue indigo. This preparation would be impossible without these special microbial! reactions.

Another example of the chemical activity of microbes is furnished in the preparation of opium for smoking. The juice of the poppy, from which opium is derived, was till lately fermented in tubs to give it the desired qualities. Recently M. Calmette, of Saigon, discovered that this transformation was due to the Aspergillus, a fungus allied to the microbes. Since then it has been enough to sow the tubs in which the fermentation proceeded with the pure Aspergillus to obtain a better return and an opium of superior quality in only one or two months.

In the preparation of several most indispensable alimentary products certain micro-organisms, domesticated as it were, prove themselves incomparable chemists. Without them these preparations would be impossible. Among such products are bread, alcohol, wine, beer, and such fermented substances as koumiss, cheese, and sauerkraut.

These microbes are inferior algæ formed of one cell, usually with an envelope. They live almost everywhere on and with living beings, in the ground, in water, on solids, etc., and multiply with extreme rapidity. They produce a great variety of actions, some of which, as we have seen, are beneficial, while others are injurious.

As microbes decompose dead matter, so they are capable of disorganizing living matter. Some species have this power in a marked degree, which is distinguished as virulence. They are called pathogenic microbes, which means capable of causing illness. Each species of pathogenic microbe produces a particular kind of disease, and has a power that varies considerably according to a number of circumstances. The microbe alone, however, can not produce disease: that requires the intervention of the organism of the subject in which the disorder is to be developed. The disease is, in fact, the resultant of the reaction of the one upon the other of the two factors, the microbe and the organism. According to the felicitous comparison of Prof. Bouchard, the organism is a strong place, the microbe is its assailant, and the struggle between them is the infectious disease. The condition of the organic estate which the microbe endeavors to seize is therefore important. If the person is in general good health, he will offer a vigorous resistance to the microbes. If, on the other hand, his health is not perfect, there will be a point where the defenses are weak, and his danger will be proportionately great; for, as M. Bouchard said some time ago, one does not become ill till he is already not in good health. There are many ways of getting into poor health. It may be done by a number of processes, which may be summarized under the two categories of troubles of the organic functions or lesions of the tissues. Some of these pathogenic processes depend directly on a variety of social influences.

Wealth and poverty are alike efficient factors of disease. The rich man, by his often superabundant diet, his neglect of exercise, and his excess of luxury, readily contracts obesity, gout, or diabetes; his kidneys and his heart are frequently afflicted with disorder. The poor man, by different forms of inanition, overwork, exposure, or uncleanliness, is liable to derangements of the lungs, liver, kidneys, bowels, etc. Like the rich man, he has a pathology special to certain organs, and different from that of the other, but which is due to his social sanitary situation.

The professions also entail their special maladies, which are liable to infect those who exercise them. Lead chemically poisons those who handle it—painters, printers, white-lead makers, etc.—and mercury is dangerous to silverers of glass and gilders; while each poison affects particular organs most directly—lead the kidneys, bowels, and brain, mercury the brain and nerves. Examples might be multiplied to show how the profession may injure the organs, create real diseases, or induce an imperfect condition of health which will facilitate the invasion of the microbe. It is not necessary to dwell here on the pathogenic effects of alcoholic intoxication—a condition which is in every feature the product of social influences. It ravages all classes of society, and is illustrated in the most various pathological modalities.

In short, we find that a great multiplicity of mechanisms, all of social origin, may affect the internal organs in their structure or their work, and bring the person into a condition of receptivity to microbes. A thousand social conditions may expose us to the invasion of microbes and thus make real the second term required to constitute an infectious disease. The hostile microbe is in fact everywhere—within and without us, seeking, we might say, what it may devour. All the natural cavities of the body—the nose, the mouth, and the digestive tube—having exterior openings are seeded with microbes brought from without by air or food, and afterward multiplied. The skin is similarly exposed. Among these microbes there are also others, the relics of infectious diseases, with which the subject, now well, has been formerly attacked. All these microbes live in the normal condition of a later life; they are sometimes useful, as we have seen in regard to digestion; more frequently inoffensive in the face of the resistance opposed to them by the cellular coverings of the organic cavities or by the activity of those zealous defenders of the organism, the white globules, or by the chemical action of the organic liquids. But when the texture of these coverings is modified by some of a variety of circumstances, whether of external or of internal origin, or when one or more of the microbes attain an unusual degree of virulence, then the protective barriers will be overcome, the microbe will penetrate to the interior of the tissues, and will be able to bring on some of a great variety of diseases, from pneumonia to erysipelas, meningitis, or liver disease.

The microbes living without the organism are likewise of various origin. We have already mentioned the innumerable varieties living in the ground, in the water, and on plants, which play so many important parts. Some of them may, under many circumstances, borrow a pathogenic power and produce diseases. There are also others, normally pathogenic, which have been eliminated from diseased organisms, and instead of succumbing at once they have fallen into the outer world, have adapted themselves to the new medium, and are living another life in the ground or in water. They are all ready when, with food or by respiration, or by a scratch of the tissues, they enter a living organism anew, to determine in it, if circumstances are favorable, the disease characteristic of them. So do the microbes of cholera, tetanus, etc. Social influences play an important part also from this point of view. All kinds of microbes may be carried to long distances by the solid matters of every kind that are employed in innumerable ways in the life of society. The solids may transport the microbes just mentioned as living in the external medium, and also those which come direct from a diseased subject. This distribution of agents of infection by solids is of extreme importance, but has attracted attention only within a few years. The hands may retain infectious germs and carry them to a long distance, often without the person carrying them being affected. Examples are abundant that illustrate the transportation and propagation in this way of pyogenic and septic infections, erysipelas, etc. Clothing, carriage cushions, tapestries, and bedding may preserve and carry cholera, smallpox, scarlatina, diphtheria, and erysipelas. The most various utensils, food, and particularly bread, may be soiled by pathogenic microbes, and thus facilitate their penetration into the organism.

We may understand, therefore, without having to insist upon it, how a large number of social circumstances may expose persons who live in society to the attacks of microbes. One's occupation will often force a person to come into contact with patients afflicted with infectious disorders, or with excreta from such patients containing pathogenic microbes, and thus cause him to contract such diseases as cholera or typhoid fever. Occupations having to do with diseased animals may also expose those who are engaged in them to direct infections, as when a groom takes care of a glandered horse; or to indirect infections, as with tanners preparing the hides of animals that had anthrax.

These examples show that there are extremely multiplied processes that may expose men living in society directly to infection by microbes, while mechanisms not less complex and equally of social origin may prepare the organic ground for the invasion of the microbe by changing either the structure or the working of the organism.

To these special causes of infectious disorders—invasion by microbes and their intra-organic evolution—hygiene is able to oppose a number of means of protection or defense; this is the part of prophylaxis. The physician can, besides, assist the organism to make a victorious struggle against the microbe; this is the part of therapeutics. On these two points, also, social influences have an extremely active effect. These interventions may be greatly modified by the position of the subject in society, and rendered, according to circumstances, insufficient and illusory, or more efficacious and even potent.

The facts thus far glanced at in this rapid review relate only to isolated cases, or to diseases which reach and kill only a few subjects. Suppose, however, these pathogenic influences raging at their extreme height; we shall then be dealing with epidemics carrying men off by thousands, by hundreds of thousands, as actually takes place with cholera, yellow fever, and the plague. Under such circumstances the microbe performs destructive work, carries death abroad, and decimates populations.

So we are brought back to the beginning of this discussion; and, examining philosophically this phase of the complex question of the office of the microbe in society, we are able to answer Broca's question, quoted at first, "What will take place in future generations when they shall have exhausted the temporary resources of emigration?" We say: Then the microbe will intervene, as it does periodically; it will decimate populations and will sow death; but it will be to renew life by enabling new existences to take the place of those which have become extinct, and by furnishing them, under an assimilable form, the organic matter which they will require for their life and healthy growth.

We thus see, even from this rudimentary sketch, that the function of microbes in society is very important. Good or evil, useful or injurious, they all have a part which is indispensable to the regular evolution of social bodies. Moreover, paradoxical as the assertion may at first sight appear, I believe the fact has been rigorously demonstrated, and may be formulated in the words, that society can not exist, live, or subsist except with the aid of the constant intervention of microbes, the great purveyors of death, but also the dispensers of matter, and therefore all-potent purveyors of life.—Translated for The Popular Science Monthly from the Revue Scientifique.


The mass of the asteroids has been computed by B. M. Roszell, of Johns Hopkins University, and found—including the whole three hundred and eleven bodies whose elements had been calculated at the time to be ·026 of the mass of the moon.
  1. An address (Conference Broca) delivered December 14, 1893, before the Anthropological Society of Paris.