86 LIFE AND DEATH. 



more particularly important in the case of applications 

 to living beings. They refer to mechanical energy, to 

 the relations of thermal energy and chemical energy, 

 to the complete role of thermal energy, and finally to 

 the extreme adaptability of electrical energy. 



1 . Transformation of Mechanical Energy. 

 Mechanical energy may change into every other form 

 of energy, and all others can change into it, with but 

 one exception, that of chemical energy. Mechanical 

 effort does not produce chemical combination. What 

 we know of the part played by pressure in the re- 

 actions of dissociation seems at first to contradict 

 this assertion. But this is only in appearance. Pres- 

 sure intervenes in these operations only as preliminary 

 zvork or priming, the purpose of which is to bring the 

 bodies into contact in the exact state in which they 

 must be for the chemical affinities to be able to enter 

 into play. 



2. Transformation of Thermal Energy ; Priming. 

 Thermal (or luminous) energy does not change 

 directly into chemical energy. In fact, heat and light 

 favour and even determine a large number of chemical 

 reactions; but if we go down to- the foundation ot 

 things we are not long before we feel assured that 

 heat and light only serve in some measure for 

 priming for the phenomenon, for preparing the 

 chemical action, for bringing the body into the 

 physical state (liquid, steam) or to the degree of 

 temperature (400 C. for instance, for the combination 

 of oxygen and hydrogen) which are the preliminary 

 indispensable conditions for the entry upon the scene 

 of chemical affinities. 



On the contrary, chemical energy may really be 

 transformed into thermal energy. We have an 



