84 Disease and Immunity 



stop for a rest. After resting for a few minutes 

 he can resume his exercise, but soon becomes 

 tired and must rest a second time. After another 

 short rest he can begin the exercise a third time, 

 and so on time after time for perhaps several 

 hours. Each period in which the man was tak- 

 ing this exercise consumed the available energy 

 in the muscles being exercised, and during each 

 period of rest the supply in the exercised muscles 

 was partially replenished by drawing upon the 

 store existing at the time in other organs. 



The fact that severely exercised muscles in 

 the arms may draw upon the reserves in unexer- 

 cised parts of the body is evident from the fact 

 that a person who has become tired by swinging 

 dumbbells is in no condition to compete in a foot 

 race or in a debating contest. Each organ has 

 in it a store of energy normally appropriated for 

 the use of that organ, but in emergency, a se- 

 verely taxed organ may draw upon the supplies 

 in other organs. 



The fact that one organ of a body when under 

 strain may call upon and receive assistance from 

 other organs represents one of the great advan- 

 tages a multicellular organism has over the uni- 



