38 THE STORY OF LIFE'S MECHANISM. 



as a foundation, we can readily explain the 

 running of the machine. Our next problem, 

 therefore, is to see if we can in the same way 

 reach an understanding of the phenomena of 

 the living machine. Can we, by the use of the 

 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 



FUNCTIONS. 



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, 



