148 THE STORY OF LIFE'S MECHANISM. 



indeed understand, but they are undoubtedly 

 chemical changes. The result is that some com- 

 pounds are pulled to pieces and part of the 

 fragments liberated or excreted, while other 

 parts are retained and built into other more 

 complex compounds. The compounds thus manu- 

 factured are retained in the cell body, and it 

 grows in bulk. This continues until the cell 

 becomes too big, and then it divides. 



If a machine is broken it ceases to carry on 

 its proper duties, and if the parts are badly 

 broken it is ruined. So with the cell. If it 

 is broken by any means, mechanical, thermal, 

 or otherwise, it ceases to run we say it dies. 

 It has within itself great power of repairing 

 injury, and therefore it does not cease to act 

 until the injury is so great as to be beyond 

 repair. Thus it only stops its motion when 

 the machinery has become so badly injured as 

 to be beyond hope of repair, and hence the cell, 

 after once ceasing its action, can never resume it 

 again. 



There are, of course, other functions of living 

 things besides the few simple ones which we 

 have considered. But these are the funda- 

 mental ones ; and if we can reduce them to 

 an intelligible explanation, we may feel that 

 we have really grasped the essence of life. If 

 we understand how the cell can move and grow 

 and reproduce itself, we may rest assured that 

 the other phenomena of life follow as a natural 

 consequence. If, therefore, we have obtained 

 an understanding of these fundamental vital 

 phenomena, we have accomplished our object 



