The Body-Machine and Its Work 341 



8 



The Large Machines of the Body 



We may seem so far only to have concerned ourselves with 

 organs which exist for the sake of other organs. That, in point 

 of fact, is the nature of every organ in the "organism"; and 

 indeed, it would be at least equally correct to say that bones 

 and muscles, which one naturally thinks of as forming the 

 greater part of the body, exist very largely for the purpose of 

 digestion and respiration. Nutrition and reproduction are 

 the oldest functions, the original functions, of the animal 

 body. The elaborate skeleton, with its masses of muscles, 

 has evolved to protect and minister to these fundamental 

 activities. 



Of the distribution of the two hundred bones and two hund- 

 red and sixty pairs of muscles which form the great bulk of 

 the body little can be said here. A catalogue of the bones would 

 be a list of unfamiliar terms; and a catalogue of the muscles 

 would be almost an essay in Greek. It is in the development and 

 minute structure of bone that modern physiology is chiefly inter- 

 ested. As is now generally known, the body begins its existence 

 as a single cell a microscopic speck of living matter surrounded 

 by a membrane and the development of the body is due to the 

 repeated and rapid multiplication of this cell (the fertil- 

 ised ovum or egg-cell), until countless millions are formed. 

 It is a "cell-state": a commonwealth of millions of living, 

 active units bound together into a harmoniously working 

 organism. 



As this "protoplasm" the jelly-like matter which composes 

 cells is soft, the beginner may wonder how it can build up such 

 structures as teeth and bones. To understand this, as far as we 

 do understand it at present, we have to remember that, as the cells 

 of the body multiply from the original egg-cell, they also separate 

 into different classes. We get muscle-cells, nerve-cells, bone- 



