68 THE STORY OF LIFE'S MECHANISM. 



with protoplasm and the living cell, since here, 

 if anywhere, can we find the life substance 

 reduced to its lowest terms. 



CHAPTER II. 



THE CELL AND PROTOPLASM VITAL 

 PROPERTIES. 



WE have seen that the general activities of the 

 body are intelligible according to chemical and 

 mechanical laws, provided we can assume as 

 their foundation the simple vital properties of 

 living phenomena. We must now approach 

 closer to the centre of the problem, and ask 

 whether we can trace these fundamental pro- 

 perties to their source and find an explanation 

 of them. 



In the first place, what are these properties ] 

 The vital powers are varied, and lie at the basis 

 of every form of living activity. When we free 

 them from complications, however, they may all 

 be reduced to four. These are: (1) Irritability, or 

 the property possessed by living matter of react- 

 ing when stimulated. (2) Movement, or the power 

 of contracting when stimulated. (3) Metabolism, 

 or the power of absorbing extraneous food and pro- 

 ducing in it certain'chemical changes, which either 

 convert it into more living tissue or break it to 

 pieces to liberate the inclosed energy. (4) Repro- 

 duction, or the power of producing new indi- 

 viduals. From these four simple vital activities 

 all other vital actions follow ; and if we can find 



