Disease and Immunity 85 



cellular. In multicellular organisms, strain is 

 never thrown directly upon all of the organs of 

 the body at the same time, and those not under 

 strain can help those which are. And mental 

 powers are not exceptions. They may be ex- 

 pended as common foot pounds through other 

 organs. 



When a man takes up a course of physical 

 training, or does other work which is more than 

 has been customary or habitual with him, but an 

 amount which is less per day that his system can 

 restore from the food he consumes, he not only 

 gets back the energy he expended, but a little 

 more. The result is that he gains some in 

 strength and endurance and can do a little more 

 work on the second day that on the first one. If 

 he gradually increases his work as his powers 

 develop he can continue to gain up to some point 

 which has never been determined. 



But if the man expends a little more energy 

 per day by his exercise than his system is capa- 

 ble of restoring from food, then he is a little 

 weaker the second day that he was the first. 

 If he repeats this operation day after day, he 



