126 APPLICATION OF METHOD IX INFECTIOUS DISEASES 



disturbances ; and we might certainly expect secondary 

 disturbances in the harmonic processes of the whole 

 metabolism of the host, without the micro-organisms 

 as such exerting any direct action. 



Finally, we have to consider yet another possibility, 

 that certain micro-organisms produce poisonous 

 substances within themselves, and give them off 

 externally. It is, at present, very problematical, what 

 view we are to take of these substances. Are they 

 substances which play a part in the metabolism of 

 the micro-organisms themselves, or are we dealing 

 with agents which, when passed to the exterior, affect 

 the nutritive medium in some way or another, that 

 is, by either decomposing or reconstituting it? It is 

 quite conceivable that certain micro-organisms have 

 agencies at their disposal, which are able to modify 

 particular nutritive cultures in a particular way. 

 Many pathological observations have proved, that 

 certain micro-organisms require a so-called mixed 

 infection, that is, that certain bacteria alter the cell 

 substance of the host in such a way, that some other 

 kind of bacterium finds conditions favourable for its 

 existence. It seems that this is also the case with 

 some kinds of tumours, such as sarcoma and carci- 

 noma, where a preparation of the medium by certain 

 substances is of great importance. In the future we 

 shall be compelled to appreciate all these possibilities. 

 If we could succeed in limiting more precisely the 



