ACTION OF FORCES ON ORGANISMS. 43 



germ in its proper environment is caused to live 

 and develop by the action of the same forces that 

 have acted on the germs of its ancestors for an 

 immense number of generations, and caused the 

 development of each in turn. If the forces be 

 altered beyond certain narrow limits, or removed, 

 then malformation, arrested development, or death, 

 is the result. 



It is impossible for us to observe, or to imagine 

 with any degree of accuracy, the action of the 

 forces which affect the organism while it is yet 

 within the membrane of the egg. We know, how- 

 ever, that these forces must act almost exactly 

 alike for all individuals of the same race. This is 

 shown by the similarity of the results. But when 

 the organism comes out of the egg-membrane, — 

 is hatched or born, — it is still lacking a large part 

 of its complete development. During this later 

 period of development we can trace to some extent 

 the particular effects of some of the forces which 

 cause development. Of the first importance in 

 this respect is the food of the organism. Without 

 thii, of course, no growth nor development would 

 occur. The quantity and quality of food seem 

 also to have a decisive effect on the degree and 

 direction of development, beside influencing the 

 general strength and activity of the organism. The 



