Physiology of Microbes. 23 



their living at the e^xpense of the nutritive residue of 

 those which have preceded them. 



2. Disassimilation, excretions, secretions. — From the 

 preceding considerations it results that disassimilation 

 in microbes ought to give very varied residues. These 

 residues naturally depend upon the food, upon the 

 species of germ, and upon the special conditions in 

 which their evolution is accomplished (temperature, 

 aerobic or anaerobic nature, etc.). 



Of these residual or excrementitial products of mi- 

 crobes some are gaseous (carbonic acid, hydrogen, car- 

 buretted hydrogen, sulfuretted hydrogen, ammonia), 

 some volatile (trimethylamin, alcohol, formic, acetic, 

 butyric acids, etc.), some fixed (lactic and malic acids, 

 leucin, taurin, tyrosin, etc., etc.). 



The nutrition of germs may give rise to coloring 

 matters, such germs being called chromogenic. The 

 coloring matter thus produced may be soluble or in- 

 soluble ; in the former case it diffuses in the fluid 

 media in which the germs occur, an instance of which 

 may be seen in the germ of blue milk. 



Among the number of the substances resulting 

 from the nutrition of microbes we have to mention 

 the ptomaines. 



Ptomaines are ammoniacal compounds acting the 

 part of bases, and which, upon the higher beings, 

 have often effects analogous to those of the vegetable 

 alkaloids, which they resemble in every respect. 



In a general way the residual products are noxious 

 to the germs from which they spring : 0.8 per cent of 

 free butyric acid arrests the butyric fermentation of 

 lactate of lime. 



The diastases must also be cited among the products 



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