LIFE IN NATURE. 



which contribute to this end do so by first exciting 

 chemical activity. Where the latter is not present, 

 no amount of other force suffices to induce the vita- 

 lizing process. And so far from these other forces 

 being always absorbed when growth is in progress, 

 we see a notable instance of the contrary in the ger- 

 mination of the seed, which is attended with a decided 

 rise of temperature. It appears that here the amount 

 of chemical change is in excess of the vital action 

 consequent upon it, and that, therefore, while a part 

 of the force it generates goes to reproduce the vital 

 state, and bring about the growth of the young plant, 

 part of it passes off as heat. So too, in some of the 

 functions of the animal (muscular motion, for ex- 

 ample), the decomposition of the tissues seems to 

 generate more force than the function consumes, and 

 the temperature rises. 



The part played by the various other forces which 

 are known to contribute to the process of vitalization 

 (of which heat and light are the chief) would seem, 

 therefore, to be either that of furnishing the condi- 

 tions for chemical action, or of adding to its intensity. 

 In both these ways their influence is essential. The 



