After the example of Liebig in 1870, Dr. Bastian did not accept the challenge.
But if a disease like splenic fever is carried by a microbe, this microbe is under the influence of the medium in which it finds itself. It does not develop everywhere. Easily inoculable and fatal to the ox, the sheep, the rabbit, and the guinea pig, splenic fever is very rare in the dog and in the pig. These must be inoculated several times before they contract the disease, and even then it is not always possible to produce it. Again, there are some creatures which are never assailable by it. It can never be taken by fowls. In vain they are inoculated with a considerable quantity of splenic blood; it has no effect upon them. This invulnerability had very much struck Pasteur and his two assistants, Joubert and Chamberland. What was it in the body of a fowl that enabled it to thus resist inoculations of which the most infinitesimal quantity sufficed to kill an ox? They proved by a series of experiments that the microbe of splenic fever does not develop when subjected to a temperature of 44° Centigrade. Now, the temperature of birds being between 41 and 42 degrees, may it not be, said Pasteur, that the fowls are protected from the disease because their blood is too warm—not far removed from the temperature at which the splenic fever organism can no longer be cultivated? Might not the vital resistance encountered in the living fowl suffice to bridge over the small gap between 41-42, and 44-45 degrees? For we must always allow for a certain resistance in all living creatures to disease and death. No doubt, life to a parasite in the body of an animal would not be as easy as in a cultivating liquid contained in a glass vessel. If the inoculating microbe is aerobic, it can only be cultivated in blood by taking away the oxygen from the globules, which retain it with a certain force for their own life. Nothing was more legitimate than to suppose that the globules of the blood of the fowl had such an avidity for oxygen that the filaments of the splenic parasite were deprived of it, and that their multiplication was thus rendered impossible. This idea conducted Pasteur and his assistants to new researches. 'If the blood of a fowl was cooled,' they asked, 'could not the splenic fever parasite live in this blood?'
The experiment was made. A hen was taken, and, after inoculating it with splenic fever blood, it was placed with its feet in water at 25 degrees. The temperature of the blood of the hen went down to 37 or 38 degrees. At the end of twenty-four hours the hen was dead, and all its blood was filled with splenic fever bacteria.
But if it was possible to render a fowl assailable by splenic fever simply by lowering its temperature, is it not also possible to restore to health a fowl so inoculated by warming it up again? A hen was inoculated, subjected, like the first, to the cold-water treatment, and when it became evident that the fever was at its height it was taken out of the water, wrapped carefully in cotton wool, and placed in an oven at a temperature of 35 degrees. Little by little its strength returned; it shook itself, settled itself again, and in a few hours was fully restored to health. The microbe had disappeared. Hens killed after having been thus saved, no longer showed the slightest trace of splenic organisms.
How great is the light which these facts throw upon the phenomenon of life in its relation to external physical conditions, and what important inferences do they warrant as to the influence of external media and conditions upon the life and development of living contagia! There have been great discussions in Germany and France upon a mode of treatment in typhoid fever, which consists in cooling the body of the patient by frequently repeated baths. The possible good effects of this treatment may be understood when viewed in conjunction with the foregoing experiment on fowls. In typhoid fever the cold arrests the fermentation, which may be regarded as at once the expression and the cause of the disease, just as, by an inverse process, the heat of the body arrests the development of the splenic fever microbe in the hen.
FOWL CHOLERA.
If fowls are naturally impervious to the infection of splenic fever, there is a disastrous malady to which they are subject, and which is commonly called 'fowl cholera.' Pasteur thus describes the disorder:—'The bird which is attacked by this disease is without strength, staggering, the wings drooping. The ruffled feathers of the body give it the shape of a ball. An overpowering somnolence takes possession of it. If forced to open its eyes, it appears as if it were awakened out of a deep sleep. Very soon the eyelids close again, and generally death comes without the animal changing its place, or without any struggle, except at times a slight movement of the wings for a few seconds.' The examination after death reveals considerable internal disorders.
Here, again, the disease is produced by a microscopic organism. A veterinary surgeon of Alsace, M. Moritz by name, was the first who suspected the presence of microbes in this disease; a veterinary surgeon of Turin, M. Peroncito, depicted it in 1878; a professor of the veterinary school of Toulouse, M. Toussaint, recognised it, in his turn, in 1879, and sent to Pasteur the head of a cock which had died of the cholera. But, however skilful they were, these observers had not succeeded in deciding the question of parasitism. None of them had hit upon a suitable cultivating medium for the parasite, nor had they reared it in successive crops. This, however, is the only method of proving that the virulence belongs exclusively to a parasite.