IS THE BODY A MACHINE ? 57 



Now what is the significance of all these facts 

 for our discussion ? Together they point clearly 

 to the conclusion that nervous energy is corre- 

 lated with other forms of physical energy. Since 

 the nervous stimulus is started by other forms of 

 energy, and since it can, in turn, modify ordinary 

 forms of energy, we cannot avoid the conclusion 

 that the nervous impulse is only a special form 

 of energy developed within the nerve. It is a 

 form of wave motion peculiar to the nerve sub- 

 stance, but correlated with and developed from 

 other types of energy. This, of course, makes 

 the nerve simply a bit of machinery. 



If this conclusion is true, the development of 

 a nerve impulse would mean that a certain por- 

 tion of food is broken to pieces in the body to 

 liberate energy, and this should be accompanied 

 by an elimination of carbonic dioxide and heat. 

 This is easily shown to be true of muscle action. 

 When we remove a muscle from the body it may 

 remain capable of contracting for some time. By 

 studying it under these conditions we find that 

 it gives rise to carbonic dioxide and other sub- 

 stances, and liberates heat whenever it contracts. 

 As already noticed, in the respiration experi- 

 ments, whenever the individual experimented 

 upon makes any motions, there is an accompany- 

 ing elimination of waste products and a develop- 

 ment of heat. But this does not appear to be 

 demonstrable for the actions of the nervous 

 system. Although very careful experiments 

 have been made, it has as yet been found impos- 

 sible to detect any rise in temperature when a 

 nerve impulse is passing through a nerve, nor is 



