158 PHYSIOLOGY AND NATIONAL NEEDS 



of their diet, but by the natural process of muscular 

 activity in the open air, the appetite with its likes 

 and dislikes acting as the guide in questions of 

 food. 



The Cutaneous System plays an important part 

 during muscular work, for the secretion of sweat 

 and the flushing of the skin with blood prevent 

 any abnormal rise in the temperature of the body. 

 The skin is moreover the largest sensory area of 

 the body, and exercise in the open air exposes it to 

 heat and cold. In such a manner accommodation 

 to changes of temperature is developed. This is 

 called the " hardening process," and possesses a 

 sound basis. Some of the beneficial effects of sun- 

 light are known, but much remains to be discovered. 



There is no time for a more detailed consideration 

 of the effects of physical training and the open-air 

 life. There are, however, a few points which must 

 be mentioned. The living body is constantly com- 

 pared with a machine, and the effects of work are 

 considered from that point of view. It is forgotten 

 that the body is more wonderfully and perfectly 

 made than any machine. It possesses the power 

 of self -adjustment and repair ; with use it grows 

 and becomes stronger and at the same time more 

 economical in its working. It cleanses itself and is 

 self-guided to supply the energy requisite for its 

 work and the rest necessary for its restoration. It 

 has a range of adaptation to different kinds of 



