Physiology of Microbes. 31 



up in nature at the expense of the solar heat, sub- 

 stances whose production requires a certain expendi- 

 ture of force. It is in these endothermlc subtances 

 that the lower organisms implant themselves. From 

 the energy which they find there stored up they bor- 

 row a portion for the construction of their own tis- 

 sues, which renders them up to a certain point inde- 

 pendent of external conditions. Another portion is 

 used to convert into the gaseous condition substances 

 originally fluid or solid. Another, finally, is trans- 

 formed into sensible heat and serves to elevate the 

 temperature of the fluid in which all these phenomena 

 occur, and, as a consequence, to accelerate their pro- 

 duction." (Duclaux.) 



To accomplish this immense work the ferments are 

 endowed with an intense destructive power, and ope- 

 rate, thanks to the rapidity of their multiplication, in 

 innumerable legions. 



We must here briefly refer to fermentations and 

 putrefaction. 



Fermentations. — Fermentations are always the result 

 of the intervention of micro-organisms. They consist 

 in modifications of special organic substances tending 

 to the formation of simpler products in which the heat 

 of total combustion is less than that of the ferment- 

 able substances from which they are derived. The 

 difference between these quantities of heat represents 

 the amount of energy appropriated by the germ for 

 its nutritive requirements, and the reaction by which 

 the fermentation is characterized has no other object 

 than the liberation of this energy. 



Fermentable substances are comparatively few in 

 number ; they are usually bodies rich in oxygen — 



