IS THE BODY A MACHINE? 41 



by the kidneys. In the kidneys are a large num- 

 ber of bits of living matter (kidney cells), which 

 have the power of seizing hold of the urea as the 

 blood is flowing over them, and after thus taking 

 it out of the blood they deposit it in a series of 

 tubes which lead to the bladder and hence to the 

 exterior. The bringing of this ash to the kidney 

 cell is a mechanical matter, based simply upon the 

 flow of the blood. The seizing of the urea by 

 the kidney cell is a vital phenomenon which we 

 must waive for the moment. 



Up to this point in the analysis there has been 

 no difficulty, and no one can fail to agree with 

 the conclusions. The position we reach is as fol- 

 lows: So far as relates to the general problems of 

 energy in the universe the body is a machine. It 

 neither creates nor destroys energy, but simply 

 transforms one form into another. In attempt- 

 ing to explain the action of the machine, we find 

 that for the functions thus far considered (some- 

 times called the vegetative functions) the laws 

 of chemistry and physics furnish adequate ex- 

 planation. 



We must now look a little further, and question 

 some of the functions the mechanical nature of 

 which is less obvious. The whole operation thus 

 far described is under the control of the nervous 

 system, which acts somewhat like the engineer of 

 an engine. Can this phase of living activity be 

 included within the conception of the body as a 

 machine ? 



Nervous System. When we come to try to apply 

 mechanical principles to the nervous system, we 

 meet with what seems at first to be no thorough- 

 fare. While dealing with the grosser questions of 

 chemical compounds, heat, and motion, there is 



