26 MAN, — THE ANIMAL 



can trace food nearly up to the living condition 

 but not entirely. It is easy to note the wastes of 

 vital activity, but no one knows just how the vital 

 energy is produced. All understand that vital 

 energy is sustained by furnishing the proper 

 amount of food. When this is lacking, the living 

 body begins to eat itself, as is shown by starvation, 

 but "when death from starvation at length comes, 

 the old flag — the flag of life — is still flying." 



We know something of the chemical agents that 

 accelerate the digestive changes in food. We do 

 not know quite as much about the chemical bodies 

 (technically called enzymes), that render the 

 digested food still more complex, until it approxi- 

 mates the complexity of protoplasm. We know 

 practically nothing of the agents that cause living 

 protoplasm to give off wastes. These several proc- 

 esses, embodied under the Law of Metabolism, 

 serve to mark off sharply the activities of living 

 things from all forms of activity in non-living 

 matter. 



10. The Law Governing the Fate of Dead 

 Bodies. — Ultimately all forms of life die, and yet 

 the surface of the earth is not cumbered with 

 them as it must have been had they retained their 

 living shape and size after death. An orderly 

 series of changes occurs which breaks down the 

 chemical bodies in dead organisms and the ma- 

 terial substance of the dead amoeba or man is re- 



