TEXT-BOOK OF BACTERIOLOGY. 145 



But there are more serious objections to it. Fliigge and Siro- 

 tinin have discovered that pathogenic bacteria in their artificial 

 cultures do, in fact, produce substances which, sooner or later, put 

 an end to their further increase. But in such cases we have noth- 

 ing- but an excess of accumulated alkali or acid, and Fliigge is cer- 

 tainly right when he says such substances have a very poor chance 

 of lasting for any length of time in a living organism and of grant- 

 ing permanent immunity. 



However, one must not regard the results of test-tube experi- 

 ments as necessarily applicable also to living animals. Nothing 

 can disprove the supposition that the same bacteria may produce 

 very different substances in two such very different cases, and that 

 we have been unable hitherto to find out the difference between the 

 substances in consequence of their intricate composition or delicate 

 nature. 



But if we grant this, the second part of Flugge's objection loses 

 most of its force,, although it may be difficult, with our present 

 knowledge of such matters, to conceive how chemical substances 

 can remain for an unlimited time in the body. On the other hand, 

 there exist no convincing proofs that such cannot be the case. 



We may suppose that we have here to deal with substances 

 very difficult to dissolve or to diffuse. Such, for instance, are the 

 albuminoids, which therefore can only be excreted slowly and im- 

 perfectly and do not disappear from the organism for some time. 



The presence and action of such substances is further rendered 

 probable by the fact that the immunity does not follow immedi- 

 ately upon the inoculation, but that days or even weeks must 

 elapse before the former has been developed to its full extent; that 

 is, the time required for the solution of a requisite quantit} r of the 

 chemical substances introduced. That this process is not accom- 

 plished without difficulty is evident from the considerable increase 

 in the temperature of the body the " inoculation fever " which gen- 

 erally occurs, and the importance of which for the production of 

 immunity has recently been insisted on by Gamaleia. Another 

 portion of these substances which remains for a time unaffected 

 is gradually brought to solution and absorbed or excreted, thus 

 producing an enduring immunity. 



The hypothesis of retention is able to explain all the phenomena 

 hitherto observed, possibly not in its original form, but yet un- 

 altered in its main features. Until a better theory is found to re- 

 place it, it may continue serviceable in many cases and may reckon 

 on our support. 



Many persons, however, are not satisfied with such a simple ex- 



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