INTRODUCTION 21 



in all of which the relations of individuals are 

 conspicuous. 



Finally, in that environment provides the sur- 

 rounding conditions for a given action, we recog- 

 nize that the body itself maintains the proper 

 environment for many of its processes. Instead of 

 depending upon fluctuating atmospheric tempera- 

 tures, birds and mammals maintain a constant 

 body temperature which is favorable for their 

 vital processes and maintains a constant rate of 

 metabolism, other things being equal. When ex- 

 ternal conditions or individual activities demand 

 greater loss of heat, the sweat glands become more 

 active, more blood reaches the surface, and the 

 body cools itself. The accumulation of waste prod- 

 ucts in the tissues results in more rapid beating 

 of the heart and more rapid respiration, so that 

 elimination is hastened. Every organ of the body 

 responds best to certain conditions, and the normal 

 body provides optimum conditions for the per- 

 formance of its various organs, thus constituting 

 an internal environment. It is impossible, of 

 course, thus rigidly to separate organic responses, 

 for everything that the organism does is a product 

 of the coordinated body; the internal environment 

 plays a part in every action and the activities of 

 every organism are closely linked with all three 

 phases of its environment. 



From the moment of conception an organism 



