78 PHYSIOLOGY 



conversely, are on a cold day impelled to move about. 

 The mouse and sparrow, their surface whence bodily 

 heat escapes being so large relatively to the small 

 bulk meted to their furnace, exhibit in cool surround- 

 ings greater tendency to move about than do large 

 animals such as the ox and vulture. And these 

 movements have the appearance of a conscious motive. 

 Yet the part of the brain employed in the automatic 

 regulation of body temperature is not that part to whose 

 activity the sensations and processes we can introspect 

 are adjunct. 



And this automatic unconscious work of regulation is 

 typical of the greater part of the work of a large portion 

 of our nervous system a portion constantly active in pro- 

 cesses quite imperceptible to our minds, imperceptible even 

 if we try to direct the attention of our mind toward them. 



But though this regulation of the body temperature 

 is automatic, and occurs in us without our consciously 

 guiding it, it nevertheless is obviously calculated to benefit 

 and to protect the vital machinery from harm. The same 

 is true of all physiological reactions. They are adjust- 

 ments to environmental vicissitudes, and are adapted 

 to conserve the well-being of the organism. Darwin 

 showed how the wide-spread existence of this property 

 of utility in bodily reactions can be explained as adapta- 

 tions under what he termed ' natural selection*. To 

 know somewhat of the 'purpose' if I may be allowed 

 that term in this connexion which the reaction serves 

 is of much help in studying a physiological reaction. 

 But physiologists, though aware of the potency of such 

 assistance, are rightly cautious in resorting to it, since 

 the 'purpose' of the reaction is often, in our present 

 meagreness of knowledge, very difficult to decipher, 

 and mistakes may be made regarding it. 



