ENERGY IN BIOLOGY. II3 



returns to the physical world. This return takes 

 place (with certain exceptions which will be presently 

 indicated) under the ultimate form of thermal energy. 

 This we are taught by experiment. The phenomena 

 of functional activity are exothermal. 



Real vital phenomena thus lie between the chemical 

 energy which gives rise to them, and the thermal 

 phenomena to which they in their turn give rise. The 

 place of the vital fact in the cycle of universal energy 

 is therefore completely determined. This conclusion 

 is of the utmost importance to biology. It may be 

 expressed in a concise formula which sums up in a 

 few words all that natural philosophy can teach as to 

 energetics applied to living beings. " Vital energy is 

 a transformation of chemical energy into thermal 

 energy." 



Exceptio7is. — There are some exceptions to the 

 rigour of this statement, but they arc not many in 

 number. We must first of all remark that it applies 

 to animal life alone. 



In the case of vegetables, looked at as a whole, the 

 law must be modified. Their vital energy has another 

 origin, and another final form. Instead of being the 

 destroyers of chemical potential energy, they are its 

 creators. They build up by means of the inert and 

 simple materials afforded them by the atmosphere 

 and the soil, the immediate principles by which their 

 cells are filled. Their vital functional activity forms by 

 synthesis of the reserves, carbo-hydrates (sugars and 

 starches), fats, albuminoid nitrogenous materials — that 

 is to say, the same three principal categories of foods 

 as those used by animals. 



And to return to the latter, it should be observed 

 that thermal energy is not the only final form of vital 



