122 APPLICATION OF METHOD IN INFECTIOUS DISEASES 



the cells of the host catch the secreted ferments of 

 the micro-organism, or render them inactive in some 

 other way, and in this manner either increase the 

 difficulties of existence for the invaders, or else com- 

 pletely destroy them. 



How sensitive individual organisms are, in regard 

 to these nutritive substrates, is shown, by numerous 

 laboratory observations on the cultivation of the 

 most varied micro-organisms. We know that 



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many of them only thrive, when very definite sub- 

 strates are offered to them. The fact, that an altera- 

 tion of the nutritive medium deprives certain organ- 

 isms of their means of existence, is shown in the 

 clearest manner by the observation that an infection 

 with trichophyton fungi cures itself at the time of 

 puberty. Evidently the cells of the skin become so 

 modified, at the onset of sexual maturity, that the 

 substrate of the host the components of the skin- 

 can no longer act as a means of subsistence for the 

 fungus. From this point of view we may well imagine 

 that medicines and other therapeutical means effect 

 a curative action, without directly attacking particular 

 kinds of cells which may be living as parasites in the 

 animal organism, for they need only to destroy the 

 conditions of existence required by the organism in 

 question by means of a modification of its nutritive 

 substrate. It is imaginable that certain means do 

 modify certain cells to such an extent, that their com- 



