CHAPTER IV 

 THE OKGANS AND CELLS OF THE BODY AT WOEK 



The understanding of a mechanism involves more than a 

 knowledge of its structure; we must study the mechanism 

 at work, and the human mechanism, which we are studying, 

 may be regarded as a factory in which work is done. 



The work of some manufacturing establishments consists 

 in separating useful constituents of the raw material from 

 useless constituents, as where kerosene is refined from crude 

 petroleum; that of others consists in producing chemical 

 changes in the raw material, as where soap is made from fat 

 or oil; while that of a third class consists in the application 

 of power by machinery, as where lumber is sawed, planed, 

 turned, or molded into the material of which houses are 

 constructed. The work of a factory, in other words, is either 

 a process of refinement or the production of a new substance or 

 the application of power. 



The human body is a factory which presents in its activities 

 examples of all three of these processes. A large part of 

 digestion is a process of food refinement ; out of the food we 

 eat the very substance of the body itself is formed; while 

 all muscular work, including the beat of the heart, consists 

 in the application of power to accomplish useful ends. This 

 work is done chiefly by the two kinds of organs whose struc- 

 ture we have just studied, namely glands and muscles ; and 

 just as their structure presents a fundamental similarity of 

 plan, so there is a fundamental similarity in the nature of 

 their activities. This can best be made clear by a somewhat 

 detailed study of each organ at work. 



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