APPLICATION OF METHOD IX INFECTIOUS DISEASES 121 



Experiments which have been carried on with 

 different so-called toxins have shown, without any 

 doubt, that splitting agents are present in them. 

 These experiments, however, do not make it 

 absolutely certain that the micro-organisms secrete 

 ferments, because it is difficult to decide whether the 

 so-called toxins of the trade represent uniform pro- 

 ducts, and particularly whether they always contain 

 secretions only. As a preliminary condition, then, 

 for the possibility of the existence of micro-organisms 

 amidst a particular complex of cells foreign to them, 

 we require the presence of ferments which enable 

 them to build up the food they require from sub- 

 stances that are in harmony with the cells and the 

 blood of their host. In this case the relations between 

 the configuration of the ferments and that of the sub- 



O 



strates are no doubt expressed in their most distinctive 

 form. How often may not a micro-organism pene- 

 trate into an organism and die out, only because it is 

 unable to feed on the nutritive medium supplied, 

 while in other cases it is able to settle down because 

 the substrates presented to it can be rendered acces- 

 sible bv its ferments. If all the substances are used 



m,' 



up, and none of the same kind are supplied anew by 

 the host at the proper place, then the conditions 

 of its existence are withdrawn from the micro- 

 organism, and it must either perish or find a new 

 'pasture.' It may also happen in many cases that 



