2i 8 THE ENGINES OF THE HUMAN BODY 



life bring within the reach of most people. Everyone, 

 by a little observation, can find out the quality and 

 quantity which best suits the working of his own machine. 

 Vegetables, fruit, and cereals will at all times provide 

 sufficient work to keep the big bowel in good order. 



Our greatest difficulty will always lie in the control and 

 management of the transport system of the great bowel. 

 Every year fortunes are made from the sale of drugs 

 which are supposed to give — and can actually give — a 

 filip to its transport system. We have seen that the 

 great bowel has its own pulsatile rhythm and its own 

 " mass-movements." They are regulated by an elaborate 

 network of nerve fibres and nerve cells placed between 

 the two strata of the muscular coat. The nervous net- 

 work is linked up with certain exchange centres in the 

 spinal cord. Through those centres the movements of 

 the great bowel may be influenced by events occurring in 

 other and even distant parts of the body. Unfortunately 

 the nervous network in the wall of the bowel is exposed 

 to certain products of absorption or of inflammation and 

 may be thus damaged. No doubt its action may also be 

 affected by substances contained in modern beverages — 

 such as the essential condiments of tea and coffee. It is 

 also true that the nervous mechanism is accessible to 

 certain drugs which can stimulate it to action, but un- 

 fortunately an artificial stimulus sooner or later comes to 

 replace the natural one and then its assistance becomes 

 a necessity. No drug can supply the place of the natural 

 stimulus. 



For the final discharge of the alimentary contents 

 a simple kind of " touch-button " mechanism is employed. 

 The act is controlled by an exchange centre established 

 in the lower part of the spinal cord. When the rectum 

 — the final chamber of the intestinal tube — has become 

 loaded by the discharge of a " mass-movement," a " call 

 of nature " arises. When the contents of the rectum 

 are forced downwards by a voluntary effort to the vent, 

 certain transmitting stations placed there are touched, 

 messages are automatically dispatched to the controlling 



