Physiology of Microbes. 21 



These are not the only diastases secreted by mi- 

 crobes. We are far from knowing all of them ; they 

 vary, naturally, according to the special nature of 

 their food. We have noted the principal of them in 

 order to bring out the general mode of the nutritive 

 process in microbes. 



II. Bespiration. 



The study of the respiration of microbes is of great 

 interest. Obviously, all require oxygen which, in ox- 

 idizing alimentary substances, supply the heat neces- 

 sary for the maintenance of life, for multiplication 

 and motion, etc. Many of them borrow it in the free 

 state from the atmosj)here or from water {aerobes), but 

 there are others which appear incapable of enduring 

 free oxygen, hence require to live protected from the 

 air {anaerobes). These last act upon certain organic 

 substances by a sort of internal combustion ; they re- 

 duce these substances into carbonic acid and into other 

 molecules generally less complex, but still susceptible 

 of oxidation, setting free a certain amount of energy, 

 as the aerobic germs on their part do by a true com- 

 bustion. 



One of the prominent characters of anaerobic germs 

 when they are nourished at the expense of quaternary 

 substances consists in the disengagement of abundant 

 gaseous products, among which we find, besides 

 carbonic acid, nitrogen, ammonia, and ammoniacal 

 compounds (trimethylamin, etc.), sulfuretted and 

 phosphoretted hydrogen, etc.; these mixtures emit a 

 peculiarly fetid odor (putrid gases). When they es- 

 pecially reduce ternary products these anaerobes give 

 as gases carbonic acid, hydrogen, and hydro-carbons. 



