248 ORIGIN AND NATURE OF LIFE 



their molecules with great speed, and its 

 energy charges accumulate so rapidly that 

 soon it passes into another phase of activity 

 automatically without any stimulus from 

 without. 



The tissues of nerve and heart muscle 

 must inevitably be arranged on the principle 

 of such short periods of fatigue and recupera- 

 tion. It would be impossible for them to 

 possess the longer periods of other tissues, 

 or recuperation, by sleep, of the body as a 

 whole would become impossible. During the 

 repose of the body as a whole, respiration 

 and circulation must be continued ; cessation 

 of either for so short a time even as two 

 minutes would lead to death of the whole 

 organism. So these shorter shifts of labour 

 and rest become developed in the balanced 

 system of their colloids. Apart from the 

 changed time interval, however, the main 

 features of the cycle are the same. Waste 

 products are produced in the active period, 

 cause fatigue, are discharged; and in the 

 resting period, fresh molecular arrangements 

 are made and energy stored for the next active 

 period. In the rhythmically active heart 

 muscle the balance of nutrient matter, of the 

 oxygen used for combustion, and of carbon- 

 dioxide formed in combustion, is set with the 



