The Body-Machine and Its Work 327 



fluous. Very few men of science agree with him, but when we 

 understand what he was driving at, we see that he had hold of a 

 very important idea. Professor Metchnikoff meant that we can 

 "digest" our food in advance by means of chemicals, and get rid 

 of all the great length of intestine which is so liable to disease. 

 At present we take in great masses of superfluous stuff, but 

 there will some day be extraordinary changes in man's diet. In 

 the meantime the organs are there and we have to feed accord- 

 ingly; but it does not follow that this will continue. 



At the base of the stomach, where the alimentary canal 

 again becomes a tube the beginning of the small (or narrow) 

 intestine there is a very powerful ring-muscle, which guards 

 the exit. Nature has provided for healthy living. The unpre- 

 pared food, if we live well, cannot run into the bowel. Mere 

 contact of food against this muscle only draws it tighter. There 

 has to be, apparently, some sort of chemical action by food 

 which is quite ready, then the muscle relaxes, and a spray of 

 the pulp shoots into the bowel. We can see the occasional gush 

 when we are following the digestion by means of X-rays. 



In the first section of the narrow intestine, the duodenum, 

 very important work goes on. Here we find a remarkable sort 

 of mechanism which has only been discovered by recent science. 

 The automatic machines of the body generally work by nervous 

 action. The sight of roast beef is "wired" to the brain by the 

 eyes, and a reflex (or reflected) nervous action sets the salivary 

 glands and the stomach glands at work. This is a sort of auto- 

 matic telegraphic system. But there is also in the body some- 

 thing like a postal service; it is one of the most wonderful 

 discoveries of modern physiology. When, for instance, the acid 

 food (or chyme) from the stomach touches the walls of the lower 

 bowel, the glands in this wall form a certain chemical (called 

 secretin) and pour it into the blood. The blood takes it rapidly 

 all over the body, but there is only one organ (or perhaps two) 

 waiting for it. In this case the pancreas (or sweetbread) receives 



