zoo THE ENGINES OF THE HUMAN BODY 



collected and poured into the duodenum by a special 

 system of ducts. We shall come back again to this 

 remarkable example of a postal system — a system which 

 is widely employed in co-ordinating the work of the 

 human machine. Acid chyme not only sets the pancreas 

 working, but, as we have already seen, causes the pylorus 

 to shut, thus preventing any further addition to the 

 duodenum until the pancreatic juice has neutralised the 



TO LIVER 



BILE DUCT 

 DUODENUM 



VE/NS FROM GREAT BOWEL 

 VEINS FROM SMALL BOWEL 

 PANCREATIC DUCT 



COMMON ORIFICE 



Fig. 41. — Part of the duodenum, with pancreas and bile duct. 



preceding batch of chyme. By this simple mechanism 

 Nature has contrived to regulate the flow of chyme from 

 the stomach according to the rate at which the pancreatic 

 juice is able to deal with it. 



The arrival of chyme in the duodenum not only sets 

 up an activity in the pancreas but also in a neighbouring 

 chemical factory — the largest in all the body — the liver. 

 It, too, represents an outbuilding or outgrowth from the 

 bowel. At a very early stage in the formation of the 

 human body, when the embryo is little over a quarter of 

 an inch in length, we can see the liver being formed by 

 a bulging out of the duodenal wall. The living micro- 



