Disease and Immunity 83 



some increase of powers by the exercise of those 

 already in existence. A negative acquirement 

 would be by the loss of powers by idleness. Such 

 things as mutilations and sunburns are "thrust 

 characters" and not acquired characters. 



When a man winds up a spring, punches a 

 bag, runs a foot race, or performs physical labor 

 of any kind, he expends certain foot pounds of 

 energy, and foot pounds are something well 

 known in science. Those foot pounds of energy 

 come out of the muscles of the man who makes 

 the efforts, and they must be in those muscles 

 before he can expend them. 



A mathematical calculation represents an 

 operation of the intelligence. But a calculating 

 machine driven by a steam engine will do the 

 same work, and things which are equal to the 

 same thing are equal to each other. The object 

 here is to show that physical energy and mental 

 energy are special forms of that energy which we 

 know elsewhere as heat, light, electricity, etc. 



When a man swings Indian clubs or dumbbells 

 he exercises certain muscles and expends cer- 

 tain foot pounds of energy. As the swinging con- 

 tinues, he gradually becomes tired and has to 



