INTRODUCTORY 5 



from the biological point of view, is that the ratio of heat- 

 supply in summer to that in winter is as 63 : 37. 



VITAL RHYTHMS 



Since ever physiology had any meaning, men have been 

 aware of the twofold process of waste and repair that goes 

 on in the living body. On the one hand, there are as- 

 similative or constructive chemical changes, as the result 

 of which complex substances are built up ; on the other 

 hand, there are disruptive or destructive chemical changes, 

 as the result of which complex substances are broken 

 down. The two sets of processes together include most 

 of the important chemical changes in the body, which are 

 summed up in the term metabolism. There is general 

 agreement that, from the chemical point 0} mew, " the life- 

 process consists in the metabolism of proteids," as Pro- 

 fessor Verworn puts it. 



Generalising from his studies on colour sensation, 

 Professor Hering was led to regard living (physiologically 

 considered) as an alternation of two kinds of activity, 

 both induced by stimulus, the one kind of activity tending 

 to storage, construction, assimilation of material ; the other 

 kind of activity tending to explosion, disruption, and 

 disassimilation. Certain cells of the liver, for instance, are 

 kept toned-up to be makers of animal starch or glycogen 

 that is assimilation. But when the muscles of the heart 

 are kept toned-up to be continually oxidising carbon- 

 compounds in the muscle-substance that is disassimi- 

 lation. 



Generalising from his studies on nervous activities, 

 Professor Gaskell was also led to regard living (physio- 

 logically considered) as an alternation of two processes, 

 one of them a stimulated running-down or disruption 



