METHODS 91 



By empirical processes we can determine in a pathogenic 

 microbe a modification causing a diminution of virulence 

 with respect to a given species ; by inoculating an animal 

 of this species with an attenuated microbe, we produce in 

 it a light form of disease, of which it is easily cured ; the 

 animal comes out hardened and resists a second inoculation 

 from a more virulent microbe. Finally it becomes refrac- 

 tory to the attacks of the most virulent individuals of the 

 pathogenic species. 



When the sheep has been cured of anthrax we can say 

 of it what we said of the anthrax when it triumphed over 

 the sheep ; it has developed within itself the organ of resist- 

 ance to anthrax by functional assimilation. But since at 

 the same time it has breathed and grazed and excreted, it 

 has also developed the other parts of its organism along 

 with the mechanism of resistance to anthrax. The case 

 of the sheep is less simple than that of the anthrax ; but 

 once the latter is understood, the former becomes easily 

 intelligible. To speak with rigorous exactness, as we have 

 already noted, we ought not to separate the organ of resist- 

 ance to anthrax from that of respiration, mastication or 

 excretion ; if one of these partial functions should happen 

 to fail, the others also would cease. In the very general 

 language we are now using, we ought to speak solely of a 

 function of the whole the function sheep which in the 

 present case comprises resistance to anthrax. The division 

 of physiological labour will come up for study later. 



Dead Colloids, Toxins, Foods 



Instead of injecting into an animal a living being like 

 the anthrax bacteridium, we may try what will happen if 

 we introduce into the animal's interior medium some dead 

 substance. 



