IS THE BODY A MACHINE? 27 



if we can in the same way reach an understanding 

 of the phenomena of the living machine. Can we, 

 by the use of these same chemical and physical 

 forces, explain the activities taking place in the 

 living organism ? Can the motion of the body, 

 for example, be made as intelligible as the motion 

 of the steam engine ? 



Physical Explanation of the Chief Vital Func- 

 tions. The living machine is, of course, vastly 

 more complicated than the steam engine, and 

 there are many different processes which must be 

 considered separately. There is not space in a 

 work of this size to consider them all carefully, 

 but we may select a few of the vital functions as 

 illustrations of the method which is pursued. It 

 will be assumed that the fundamental processes 

 of human physiology are understood by the reader, 

 and we shall try to interpret some of them in 

 terms of chemical and physical force. 



Digestion. The first step in this transformation 

 of fuel is the process of digestion. Now this pro- 

 cess of digestion is nothing mysterious, nor does it 

 involve any peculiar or special forces. Digestion 

 of food is simply a chemical change therein. The 

 food which is taken into the body in the form of 

 sugar, starch, fat or proteid, is acted upon by the 

 digestive juices in such a way that its chemical 

 nature is slightly changed. But the changes that 

 thus occur are not peculiar to the living body, since 

 they will take place equally well in the chemist's 

 laboratory. They are simply changes in the mo- 

 lecular structure of the food material, and only 

 such changes as are simple and familiar to the 

 chemist. The forces which effect the change are 

 undoubtedly those of chemical affinity. The only 

 feature of the process which is not perfectly intel- 



