THE MANIFESTATIONS OF LIFE 



81 



So complex does this structure become in the higher 

 animals that the exact nature of the contractile phe- 

 nomena has not yet been explained. 



METABOLISM. 



The early students of biology believed that the vital 

 manifestations depended upon a special force vital 

 force peculiar to living substance. A few still adhere 



FIG. 27. Myograph, an instrument used for recording muscular contractions. 

 A frog's muscle a, is fixed by one end in the holder 6, while a thread c, is 

 fastened to the other tendon, connecting it with the weight, d. When the 

 electrode e, stimulates the muscle, the movement is recorded upon the revolving 

 drum, /. (Verwom.) 



to this belief and are called, in consequence, vitalists, but 

 an ever-increasing majority see in them nothing that 

 may not be explained by the ordinary laws of chemistry 

 and physics and are therefore known as chemico-physicists. 

 When the activities of living substance are carefully 

 studied, it is easy to determine that every activity, being 

 an expenditure of energy, is attended with molecular 

 (chemical) changes in its composition, usually in the 

 form of oxidation and analogous to the process of com- 

 6 



