102 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



The output of energy from the body machinery is 

 attended by a loss of material substance, and this 

 loss is continuous, even when that machinery is in, 

 what we call, the resting state, as in sleep, where the 

 voluntary muscles and mind are quiet. The output 

 of energy lasts as long as the spark of life is unex- 

 tinguished, because just so long must the production 

 of animal heat continue. If there are no new 

 sources of energy from food, the outflow of energy is 

 at the expense of materials which are stored, such as 

 glycogen and fat, and to a lesser extent the living 

 protoplasm itself. The need for new supplies of 

 combustible material is associated with nervous 

 impulses passing from the glandular cells of the 

 digestive organs to the central nervous system and 

 rising into consciousness as hunger. If by some 

 drug the appetite for food should be abolished, the 

 life of the organism would soon come to an end, and 

 during the period of starvation the body would live 

 on its own tissues, with a restricted output of energy. 

 So completely does self-preservation depend on the 

 appetite which respects the needs of the body cells 

 the somatic appetite as we have called it to dis- 

 tinguish it from the sexual. 



The hunger for food constitutes the chief occa- 

 sion for releasing that energy of performance which 

 we call the power of the will; for, until appetite is 



