254 MICRO-ORGANISMS AND DISEASE. [CHAP. 



level with, say, the relation of the saccharomyces to the 

 alcoholic fermentation ; as long as a solution contains sugar, 

 the saccharomyces is capable of multiplying, but as soon as 

 all the sugar has disappeared as such, i.e. has become split 

 up into alcohol and carbonic acid, the fermentation ceases, 

 the solution being now exhausted as regards the sac- 

 charomyces ; a new charge of saccharomyces put into the 

 solution is not capable of multiplication. This theory, then, 

 to explain the immunity, is generally spoken of as the 

 Exhaustion Theory. 



On careful analysis, it will be found that it is not capable 

 of explaining all the facts of the case. As we mentioned in 

 a former chapter, cattle inoculated with blood of a guinea- 

 pig dead of anthrax become affected with anthrax, which, 

 although not fatal, is nevertheless sometimes very severe. 

 The animal recovers, and is now, for a time at least, protected 

 against a second attack. But there is absolutely no ground 

 for the assumption that if any infusion of the tissues of this 

 animal were made, the bacillus anthracis sown in it would 

 not thrive luxuriantly, seeing that bacillus anthracis grows 

 on almost anything that contains a trace of proteids. Simi- 

 larly when of the tissues of a guinea-pig, or mouse or rabbit, 

 dead of anthrax, an infusion is made, and this is used as 

 nourishing material for bacillus anthracis in artificial cultures, 

 it is found that these latter thrive splendidly. The same 

 fact I have observed in the case of swine-plague. There is 

 then no reason whatever for assuming that, if after one 

 attack of illness the blood and tissues become an unfavour- 

 able soil for a second invasion of the same organism, this 

 should be due to the exhaustion 01 some necessary chemical 

 compound. 



There is another theory, commonly spoken of as the 

 Antidote Theory (Klebs). According to this, the organisms 



