2 10 MAN, THE ANIMAL 



know of no facts which estabhsh the time when the 

 peak of vigor is reached in the daily rhythm nor 

 how long it remains at this level. There is cer- 

 tainly a large range of variation in this physio- 

 logical trait. It is apparent that one can keep the 

 fact in mind and slowly train the body so as to 

 take advantage of this characteristic. There are 

 times when a big task seems impossible, which in 

 the morning resolves itself as easily as sugar-snow 

 melts before the spring sun. The whole quality 

 of ability that one is thus able to utilize is at its 

 best. 



The limitations of the daily rhythm and the 

 significance of chemical messengers are presented 

 because of their intimate and continuous regu- 

 latory influence. They are but examples of sev- 

 eral similar conditions that operate continuously 

 in shaping man's responses. It is an easy task 

 now to summarize the relations of Biology to 

 progress because we recognize the direction in 

 which they lie. 



By progress we mean the increase in the scope 

 of our actual knowledge of the laws of life, par- 

 ticularly as they apply to man. For his activities 

 are inseparably dependent on that fundamental 

 organization which he has in common with the 

 animals and which is the central theme of this 

 book. However man must do more than merely 



