Long-Tailed Jaeger Stercorcaius longicaudus (see pp. 78, 200, 247). 



J. The Background 



WHEN I ENTERED the field of physiology after World War I, 

 scientific research was beginning a period of rapid expansion. 

 Accompanying this expansion, to enlarge the scope of scientific 

 observation, was a corresponding development of increasingly com- 

 plex instrumentation. For the analysis of physiological processes 

 this instrumentation is essential, but it is most easily applied in the 

 laboratory to the reactions of domesticated animals. 



A consequence of this need to observe animals in laboratories is that 

 the physiological reactions are seldom viewed in context with the 

 natural situations in which the variety of responses evolved. In the 

 various natural situations in which each species finds itself, animals 

 have only the power of their intrinsic physiological and social proc- 

 esses with which to meet the environment and maintain the orderly 

 distribution of life. Under domestication the artificial selection that 

 produces animal varieties is exercised by processes extrinsic to natural 

 biological systems. This extrinsic process is arbitrarily applied by 

 human choice to decide the forms and associations in which life will 



