202 THE ENGINES OF THE HUMAN BODY 



thus preparing them for their conversion into soaps. If 

 the biliary function of the liver is deranged the bowel 

 experiences a difficulty in the digestion of fats. The 

 secretions of the liver and pancreas enter the duodenum 

 by a common orifice, which is guarded by a sphincter 

 mechanism (fig. 41). The bile and pancreatic juice, 

 fully a pint of each are formed daily, enter the duodenum 

 and become mixed with the chyme as it enters the great 

 intestinal factory. 



Having thus made a rapid survey of the means adopted 

 for the digestion of chyme, we now turn to the system 

 of transport which carries the chyme along the intestinal 

 tube. The system is one with which we are already 

 familiar. There are the usual two strata of muscle — an 

 outer with the spindles arranged along the length of the 

 bowel ; an inner with the spindles set in a circular manner. 

 Between the muscular strata, and closely connected with 

 them, is an elaborate nerve system, made up of nerve 

 corpuscles or cells as well as of fibres. Inside the 

 muscular coat is the lining membrane of the intestine, 

 where all the operations connected with digestion and 

 absorption are carried on. Outside the muscle coat is 

 a covering membrane — the peritoneal coat. This is 

 perfectly smooth and moist, in order that one loop of 

 bowel may move upon an adjoining loop just as freely 

 as one worm may glide over its neighbour even when 

 these are packed units of a wriggling mass. Indeed, in 

 one sense we may truthfully regard an earthworm as a 

 moving independent miniature piece of bowel. 



We have seen that the contraction waves which sweep 

 along the stomach and milk its contents into the duodenum 

 usually start from a particular centre or nodal point. 

 There are nodal points in the bowel. There is a domi- 

 nant centre in the duodenum above the entrance of the 

 pancreatic and bile ducts, where contraction waves start 

 at a rate of five or six a minute and slowly creep down 

 the duodenum, milking its contents in front of them. 

 Then, where the duodenum passes into the next part 

 of the small bowel, the jejunum, another series of driving 



