THE HUMAN BODY AS AN ENGINE. 499 



may be 100 degrees or more, and we do not know of any such difference 

 of temperature in the body. Indeed, we know, on the contrary, that the 

 temperature of the body is remarkably uniform, as already stated. It 

 is possible, however, that there are molecular differences of large 

 amount. In other words, if we could make an ultra-microscopic sur- 

 vey of temperature in a muscle during contraction, there might be 

 found places of high temperature where combustion was occurring, and 

 all the requirements of a heat engine of molecular dimensions fulfilled. 

 But this is a matter of speculation. The process may yet be found to be 

 electrical, or something else quite different from that of a steam engine. 

 We thus find between the animal body and a locomotive engine a 

 striking parallel. In many particulars the chemical and physical pro- 

 cesses going on in the latter are found also in the former. In both, the 

 fundamental law of the conservation of energy is strictly observed. 

 Nevertheless, the animal body considered simply as a machine is far 

 more complex in its structure and operation than the engine, and far 

 more of mystery envelops its working. Much remains for the chemist 

 and physicist and physiologist to reveal, and no more fascinating field 

 of research exists. 



