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bacillus introduced into a healthy animal who is susceptible will produce in it an attack of the same disease. And further, that while the bacillus lactis will excite fermentation in milk, and cannot produce splenic fever, the bacillus anthracis may fall into milk without producing any acidity.
Yet another idea presented itself apparently unbidden to the minds of some of these inquirers. In the proper sense of questioning Nature, an attempt had been made to infect a susceptible animal with splenic fever by injecting blood from a diseased animal, which, by delicate manipulation, was supposed to be freed from the germs of the bacillus, and the answer given was that, even so, a mild form of the disease was communicated. Out of this the inquiry necessarily sprang: In what consists this mild form of the disease, and what are the means by which it may be excited? Separate observations had been teaching that a given menstruum, or what is now called a nutritive fluid, ceases after a certain time to be capable of reproducing the particular form of organism for which, in the first instance, it served as a matrix. This decadence of the growth could at any period be arrested by a change in the nutritive fluid. By experiment, it has been ascertained that, during the period of degeneration, the disease produced by inoculation becomes milder and milder; while, on the contrary, it increases in intensity as the
