CYCLIC ACTIVITIES OF LIFE 243 



in addition to its external obvious secretion 

 which it pours into the intestine, possesses 

 a secret internal secretion which it pours 

 into the blood for the regulation of carbo- 

 hydrate exchanges in the body. 



These instances may suffice to demonstrate 

 the wealth of chemical sympathies existing 

 between the huge nations of living units 

 of different types which constitute our bodies, 

 and the delicacy of structure can be appre- 

 ciated which makes such highly specific 

 reactions possible. The whole subject is 

 modern, and is as yet by no means exhausted. 



CHAPTER X 



CYCLIC ACTIVITIES OF LIFE : 

 WAKING AND SLEEPING I FATIGUE AND 

 RECUPERATION 



The living cell may be regarded, from the 

 physico-chemical point of view, as a peculiar 

 energy-transformer, through which a con- 

 tinually varying flux of energy ceaselessly 

 goes on, and the whole life of the cell is an 

 expression of variations and alternations in 

 rates of flow of energy, and of swings in the 

 balance between various forms of energy. 



