3. Spirillum, or spiral, but inflexible—three species.
4. Spirochœte, spiral, but flexible—one species.
Dujardin, in 1841, in his Natural History of the Zoophytes, accepted the classification of Eherenberg, except that he unites the spirillum and spirochœte, calling them all spirillum. Up to this time all bacteria had been considered animals, but a close study of their life history and habitat by those who followed declared them to belong to the vegetable kingdom, and as such they are accepted to-day.
In 1853, M. Chas. Robin pointed out the relationship of bacteria to Leptothrix, a form of fungi closely allied to that of mildew; and M. Davaine, in 1868, clearly demonstrated their relationship to the vegetable world. From this time the progress of bacteriological investigation has made rapid strides. Prof. Pasteur in the organisms of fermentation and the role they play therein; Davaine and Hallier in demonstrating the specific relationship of bacteria with charbon or anthrax; and the work of Koch, Nageli, Kohn, Bilroth, Miguel, Burdon, Sanderson, Klein, Weigert, Klebs, Ehrlich, Sternberg, and many others, are too recent to require special mention.
Few have more than the faintest conception of the minuteness of these organisms. Prof. Cohn, justifying himself for the unscientific method of comparison which he uses in class instruction by Prof. Tyndall’s argument on the scientific use of the imagination, says he compares man to the cheese mite, as the Strasburg cathedral to a sparrow. Of the animalcules which Leeuwenhoek discovered, they are to man as the bee is to the horse. As improvements have been made in microscopes, just so fast have we penetrated into the world of micro-organisms, until now the proportion between the smallest we can see and man, is as man is to Mont Blanc.
Of course, with these exceedingly minute structures, nothing can be made out except points. Among some of the larger forms, a few have been able to see cellia, and in some cases the growth of the spores; but in the present state of microscopical optics the work is slow, and progress in this direction is waiting an advance in the science of optics.
Like all living organisms, bacteria propagate themselves. The most usual method is by fission or by partition, though Magnin and Cohn have recorded their observations on the formation of spores and sporangia, and I have myself witnessed the last named method. It is of importance to note that while the bacterium is killed by continued exposure to temperatures of freezing or 176° F., the spores will germinate after protracted exposure to temperature as high as 205° F. or as low as °123 F. These spores will also withstand complete desiccation, and it is in this form, mixed with the air we breathe and move in, that present the conditions from which all zymotic diseases originate. Miguel has shown that, while the air contains very few adult bacteria, it contains myriads of their spores. To the researches of Koch, Pasteur, and others, we are indebted for the certain information that, while these omnipresent germs withstand such vicissitudes of temperature, they require certain food for their maintenance; and though we cannot as yet tell what that food is, we know that when nutrient material is submitted to their action they thrive for a time, and when the particular principle which supports them is exhausted they die. This is particularly true of pathogenic germs, and the accepted theory of the bacillus tuberculosis, or the germ of consumption, is a good illustration. It has been demonstrated by Koch, Klein, Pasteur, Frankell, Sternberg, and others, that they require some product of inflammatory action for their support within the body of their victim. This is also true of cholera, at least so far as their dietary requirements are concerned. The animal cannot be infected with tuberculosis by merely introducing the germ-laden material into the stomach or upon any of the mucous membranes; but if an inflammatory condition be present, either due to the puncture of the introducing needle or scalpel, or to extraneous causes, such as a catarrhal condition of the lungs, tuberculosis is as sure to follow as the sun is to rise again.
The human mind can scarcely comprehend the enormous numbers of these omnipresent atoms without a resort again to the legitimate use of the imagination. A computation of the increase from a parent germ shows as follows: We know that the parent grows until it reaches double its original size, when it constricts itself in the middle like a figure eight and breaks into two individuals. Each of these divides again, and, on account of the rapidity with which this is done, we find them usually in chains or squares. The warmer the air, the faster this proceeds, and at the temperature of the body the entire life history of a germ, from the time of fission of the parent to the time of his own subdivision into two new individuals occupies less than one hour. This gives us a known quantity for our problem. Let us look at the result. From a single germ increasing by the power of two each hour, we have at the end of twenty-four hours 16,777,220; at the end of two days the number has increased to 281 billions, and in three days to the enormous number of 48 trillions, and in one week the number can only be expressed by figures of fifty-places. In order to make this number comprehensible, let us figure the mass and weight of this, the result of a single bacterium. A single Bacterium Termo has an average width of 1
1,000 mm. A cubic mm. would therefore contain six hundred and thirty-three millions, and in one day would be one-fortieth full. At the end of the following day there would be required 444,570 such cubes to contain the product of the parent, or say half a litre. Suppose the seas of the earth cover two-thirds of its surface with a mean depth of one mile, the aqueous product would be 929 million miles. Now, our parent germ and its product would in five days completely fill this space. More wonderful still is a gravimetric estimation. Suppose we call the specific weight of the parent germ the same as water, which cannot be far from right, it would appear that the parent weighs, or his equal bulk of water weighs, 136 millionths of a gramme; in forty-eight hours, 442 grammes; in three days, nearly 7½ million kilograms; and, inside of thirty days, the weight of the earth itself.
Prof. Cohn, in offering these figures, says: “I don’t consider this idle play; without it we can form no conception of not only the enormous increase, but the tremendous destruction of these germs which is going on around us. Food is lacking to support more than a comparatively small proportion of the product of the parent, and, as it is demonstrated that they feed from their environment, one can readily understand that without a constant supply a given infectious germ will with its followers soon destroy its nidus or perish from starvation.”
Our breweries demonstrate the truth of this hypothesis; for, in twenty-four hours, a single yeast cell, which is 8
1,000 mm. in diameter, will yield one hundred-weight of yeast.