RECENT STUDIES UPON IMMUNITY.' 



I. 



The jvolution of our bacterial knowledge has been so rapid during the 

 last few years, that already the ideas prevalent early in the eiglities are 

 matters of ancient history, and the theories witli regard to bacterial 

 action and the nature of immunity which then obtained are wholly out 

 of date. Yet these theories were useful in their day, and, if possessing 

 no other value, they are useful now as niai'king the progressive advances 

 of a young science. 



Based upon very scanty observations, these older theories were 

 disproved so soon as they were put to the experimental test. The 

 "exhaustion" theory of Pasteur and Klebs, that bacteria use up certain 

 materials in the economy, and that consequently further invasion and 

 proliferation is pi'evented by the absence of tlie food material necessary 

 for the growth of these bacteria, was sliown to be insufficient ulien it 

 was determined that the bacilli of anthrax would grow easily in tlie body 

 fluids of animals rendered immune to the disease, and not only in the 

 removed fluids, but also, under certain conditions, within the bodies of 

 the same animals. And Chauveau's "retention" theory, which owed 

 its origin to the fact that microbes grown outside the organism tend to 

 be destroyed by the products of their metabolism, and which supposed 

 that products of bacterial growth present in the fluids of the body pre- 

 vent a second development of the bacteria, was found to be equally weak. 

 It is in the highest degree improbable that such soluble substances 

 should not bo gradually excreted during the course of a very few days 

 or weeks. But apart from this antecedent improbability, a further 

 difficulty arises from the fact already mentioned, that microbes can grow 

 easily in the removed body fluids of animals rendered refractory. Even 

 if it be taken that the bacterial products are insoluble, then, like mercury, 

 arsenic, and other substances wliich remain unexcreted, they must be 

 stored up in certain organs, and the immunity conferred by them can 

 be but local, confined to the organ or organs in which they are deposited; 

 it cannot be generalised. 



* In reprinting this article I have t.ikon tho opportunity to make one or two rcrbal altera- 

 tions where it seemed to me that the original might be onsidered ambiguous. 



