Germ theory

“ They had been made upon pigeons with the bacteria of the swine-plague virus and their products. Since the demonstration of the germ theory of disease, it has become evident that there are three possible explanations of the action of these products: 1. Something is deposited in the body during the attack of disease that is unfavorable to the specific germ. 2. Something is exhausted which is essential to the development of the germ. 3. The living tissues acquire such a tolerance for the germ, or for a poison which it produces, that they are no longer affected by it. ”

“ The 'Germ Theory,' briefly stated, is this. There are all around us millions of micro-organisms, parasites which thrive and grow by feeding upon the animal world. In proportion as these parasities infest, and thrive upon a given individual, so will that individual become diseased, and it has been shown that in many cases a special germ will cause a special disease. I could deliver you a lecture, hours long, upon the classification, morphology, and pathogenic action of bacteria, but I wish at present to lead your mind into a different channel. ”

“ This theory, published in. 1873, claimed "in the abstraction of its promise and completeness of its conclusions to yield to none of its predecessors." Yet, even in France, the task of transforming medicine into a natural and exact science is far from being a fait accompli.
The most recent theories of disease are the result of microscopical study of germs,—the germ-theory, in fact,—and260 stand in the closest possible relation with the doctrine of spontaneous generation, fermentation, miasm, and contagion. ”

“ The phrase, which was once accurate, is now misleading, for the germ “theory” is part of the definite achievement of science. Not only have we succeeded in isolating the specific germ whose introduction into the body is responsible for different diseases, but in many cases, by studying the history and behavior of the germ, we have been able to find methods of checking its inroads, and so have delivered men from scourges like yellow fever and the bubonic plague. ”

“ The first is based upon chemical processes, the second upon the multiplication of living organisms. The chemical theory maintains that after the infectious element has been received into the body it acts as a ferment, and gives rise to certain morbid processes, upon the principle of catalysis. The theory of organisms, or the germ theory, maintains that the infectious elements are living organisms, which, being received into the system, are reproduced indefinitely, and excite morbid processes which are characteristic of certain types of disease. ”

“ Excluding the notion of vitality, in the whole range of chemical science you cannot point to an action which illustrates this perfect parallelism with the phenomena of life — this demonstrated power of self-multiplication and reproduction. The germ theory alone accounts for the phenomena.
In cases of epidemic disease, it is not on bad air or foul drains that the attention of the physician of the future will primarily be fixed, but upon disease germs, which no bad air or foul drains can create, but which may be pushed by foul air into virulent energy of reproduction. ”

“ We have only to suppose that the pathogenic bacteria, when growing as parasites in man, produce such poisons, and we have at once an explanation of the method by which they give rise to disease.
This explanation of germ disease is more than simple theory. It has been in many cases clearly demonstrated. It has been found that the bacteria which cause diphtheria, tetanus, typhoid, tuberculosis, and many other diseases, produce, even when growing in common culture media, poisons which are of a very violent nature. ”

“ Germ Theory.—The contagiousness of the communicable maladies is accounted for by the existence of the immense number of almost inconceivably small micro-organisms, which are constantly produced by and given off from the sick person, and carried through the air of a room or house either alone or attached to the innumerable epithelial scales which are all the time being rubbed off, as dandruff, etc., from our bodies. ”

“ And so far from the fully developed organism’s being simply the germ plus the nutriment, which it has absorbed, it is probable that the adult contains neither in form, nor in substance, more than an inappreciable fraction of the constituents of the germ, and that it is almost wholly made up of assimilated and metamorphosed nutriment.”
This being true, it cannot be said that the germ (fertilized ovum) ever develops into a man or woman. On the contrary it is annihilated; and its identity is wholly lost among the daughter-cells which are made of the mother’s food. ”

“ This does not ignore that the chemical products or enzymes which are constructed by the vital activity of the microbes, will dissolve or transform organic matter, but in the absence of the microbe no such enzyme can reproduce nor multiply itself and its action must therefore be exactly limited by its amount. The living germ itself is therefore the one effective factor, by which the contagious disease may be maintained and propagated. In its turn the living germ can only come from a pre-existing living germ. ”

“ The later system of Pasteur is founded on this same general truth, as are also the methods of lessening the pathogenesis of germs by subjecting them to compressed oxygen, to graduated heating, to an altered chemical condition of the culture medium, to antisepsis, etc. For a time such weakened cultures often retain their lessened pathogenesis, even through a succession of cultures in a susceptible animal body, acting as if the germ were indeed a distinct species. ”

“ The great host of species which are found in water, milk, air, in our mouths or clinging to our skin, and which are almost omnipresent in Nature, are capable of growing well enough in ordinary lifeless organic foods, but just as soon as they succeed in finding entrance into living human tissue their growth is checked at once by these antiseptic agents which are poured upon them. Such bacteria are therefore not pathogenic germs, and not sources of trouble to human health. ”

“ There are, however, some species which cause mankind much trouble by interfering in one way or another with the normal processes of life. These pathogenic bacteria, or disease germs, do not all act alike, but bring about injury to man in a number of different ways. We may recognise two different classes among them, which, however, we shall see are connected by intermediate types. These two classes are, first, the pathogenic bacteria, which are not strictly parasitic but live free in Nature; and, second, those which live as true parasites in the bodies of man or other animals. ”

“ It is therefore possible to conceive that at some time or other there has existed only one kind of germ, that variations from this one type have arisen in consequence of the modification wrought upon different individuals by their chance falling upon this or that degenerate tissue. Variation must lead to specialization, and finally we find diseases all dependent upon the action of germs, as different from one another as one species of animal differs from another. ”

“ I am also far from asserting that the germ-plasm which, as I hold, is transmitted as the basis of heredity from one generation to another, is absolutely unchangeable or totally uninfluenced by forces residing in the organism within which it is transformed into germ-cells. I am also compelled to admit it as conceivable that organisms may exert a modifying influence upon their germ-cells, and even that such a process is to a certain extent inevitable. The nutrition and growth of the individual must exercise some influence upon its germ-cells . ”

“ As a consequence, the proof of the germ nature of different diseases varies all the way from absolute demonstration to mere suspicion. To give a complete and correct list of the diseases caused by bacteria, or to give a list of the bacteria species pathogenic to man, is therefore at present impossible. ”

“ In fact, a favorable breeding ground is perhaps not second in importance to the presence of the germ itself, as the number of individual microbes, up to a certain point, which gain access to the human body, is probably of much more importance than the kind of germ. ”

“ While most of the so-called germ diseases are caused by the bacteria which we have been studying in the previous chapters, there are some whose inciting cause is to be found among organisms belonging to other groups. Some of these are plants of a higher organization than bacteria, but others are undoubtedly microscopic animals. Their life habits are somewhat different from those of bacteria, and hence the course of the diseases is commonly different. ”

“ How Disease Germs Grow.—Experiments having shown that no life is known to spring from inanimate matter, we may reasonably suppose that just as wheat does not grow except from seed, so no disease occurs without some disease germ to produce it. Then, again, we may logically assume that each disease is due to the development of a particular kind of germ. If we plant smallpox germs, we do not reap a crop of scarlatina or measles; but, just as wheat springs from wheat, each disease has its own distinctive germs. ”

“ But the everlasting wonder is, how all the characteristics of a species can be embodied in a germ so as to be reproduced by growth; and still more amazing is it how the nicer shades of organic modification are also transmitted by the germ so as to become hereditary. In some way the systems of organic molecules must be capable of taking and retaining an infinite number of inconceivably delicate impressions; for with the myriad forms of life there must be formed myriads of molecular modifications of germ structure. ”

“ Some few species, however, are not thus destroyed by the hostile agencies of the tissues of the animal, but are capable of growing and multiplying in the living body. These alone are what constitute the pathogenic bacteria, since, of course, these are the only bacteria which can produce disease by growing in the tissues of an animal. The fact that the vast majority of bacteria can not grow in the living organism shows clearly enough that there are some conditions existing in the living tissue hostile to bacterial life. ”

“ But why should not a germ disease be always fatal? If the bacteria thus take possession of the body and can grow there, why do they not always continue to multiply until they produce sufficient poison to destroy the life of the individual? Such fatal results do, of course, occur, but in by far the larger proportion of cases recovery finally takes place. ”

“ Having glanced hastily at the history of bacteriology, we may next consider some facts concerning the germs themselves. What are they? To the lay mind the words germ, microbe, bacterium, and bacillus often convey confused ideas of invisible, wriggling, worm-like creatures, enemies of mankind, ever on the watch to gain a stealthy entrance into our bodies, where they wreak harm and death. Scientifically considered, however, they are the smallest of living things yet known. They are not animals, but are members of the vegetable kingdom, and are possessed of definite yet varying shapes. ”

“ Each of these colonies of germs is under perfect control, and in many of them their natural wickedness has been so much alleviated that they are now useful aids to the doctor, who gives his patient a mild dose of the disease in order to accustom his system to resist accidental infection by the original type.
Yet what has been done already is only an earnest of what will no doubt be accomplished. Every farmer and ploughboy will in time sow his own bacteria; every dairymaid will make all sorts of cheese, from Camembert, Rochfort, to Gorgonzola, by sowing the right kind of germ upon it. ”

“ But the methods of combating the different diseases when once contracted in the human body, based on the knowledge obtained of the life history of these germs, have been the most important result of their biological study. A large part of this knowledge has been acquired by the study of animals which have been found susceptible and so available for experimental investigation, and it may be that the impossibility of studying measles, for instance, in animals, may be one reason why the germ has never been discovered. ”

“ The following statements comprise the most important facts known in regard to it, and its relation to the disease in man.
Undoubtedly the malarial germ has some home outside the human body, but it is not yet very definitely known what this external home is; nor do we know from what source the human parasite is derived. It appears probable that water serves in some cases as its means of transference to man, and air in other cases. From some external source it gains access to man and finds its way into the blood. ”

“ This is sufficient to afford a fair sample of the germ content of the mixture, and at the same time is insufficient to exert any inhibitory action when transferred to the subculture medium.
e. Subculture Medium. Bile Salt Broth.—
A fluid medium is essential in order to obtain immediate dilution of the germicide carried over; at the same time it is advantageous to employ a selective medium which favours the growth of the test germ to the [Pg 484] exclusion of organisms likely to contaminate the preparation, and if possible one which affords characteristic cultural appearances. ”

“ It is also accounted for by the germicidal properties of the blood serum.
The resistance of the tissues may in some cases be due to the absence from them of some particular element necessary to the growth of a particular microorganism. This refractoriness varies in every species of animal in its relation to every form of germ. Different individuals of one species also vary in their susceptibility, and even different parts of the body vary in the same individual. The lower animals offer a greater resistance to pyogenic bacteria than do human beings. ”