But when the treatment is begun the infected individual has already within him the disease germs and toxins; by adding to these germs and toxins we might expect on à priori grounds that the rapidity of the disease would be increased, and the fatal result rendered more certain, since the phagocytes would have less time wherein to vary fitly—to acquire the power of destroying the microbes of rabies in the presence of their toxins. The contrary, however, is the case, for under such treatment the infected individual usually recovers. This, then, is the difficulty which must be surmounted before the phagocytic theory of immunity can be accepted.
When under fit conditions yeast is introduced into a solution of grape sugar, that micro-organism multiplies rapidly. Concurrently with its multiplication, and in proportion to it, the sugar disappears, and is replaced by alcohol. Whence we may fairly conclude, that the sugar is used as food by the micro-organism, and that the alcohol is an excretion, an effete waste product, comparable to the waste products present in the excretions—e.g. urine—of higher animals. Like those waste products, it is more or less poisonous to the organism that produces it, as is proved by the fact that, when the alcohol reaches a percentage of fourteen in the solution, the yeast ceases to multiply and perishes. It was at one time thought the behaviour of yeast in a solution of sugar afforded an explanation and an illustration of the way in which immunity against microbic disease is acquired. The micro-organisms of disease were believed to produce waste products, poisonous to themselves, which were retained as in a bottle by the host, and which, therefore, when they attained a certain strength, wrought the destruction of the micro-organisms that produced them, and rendered the infected individual immune for the future, or at least for so long as the waste products were not excreted and were retained
