PREPARATION OF TISSUE-FUEL 191 



the duodenum. They are- blocked at the pylorus. The 

 pyloric gateway is not regulated by the usual form of 

 " touch-button " mechanism ; the opposite is the case. 

 When a solid body is brought down and pressed against 

 it by a contraction wave, the sphincter closes the gateway 

 more tightly. As far as we yet know, it can be man- 

 ipulated only by chemical messages or signals. When 

 the gastric juice is plentiful and markedly acid in 

 quality it yields to the contraction waves which beat 

 against it and allows a jet of gastric contents to pass. 

 But when the acid contents have thus freely entered the 

 duodenum, the sphincter again becomes recalcitrant and 

 refuses further passage from the stomach until the 

 duodenal contents have become neutralised and alkaline 

 in reaction. Thus is the pyloric sphincter automatically 

 regulated by the chemical state of the contents of the 

 stomach on the one hand, and the readiness of the 

 duodenum to receive a further load on the other. The 

 pyloric janitor is also controlled by signals which may 

 arise from other factories further down the alimentary- 

 line. It is manifest, if these factories, such as segments 

 of the small bowel or the caecum or a part of the great 

 bowel, are already overtaxed, that an addition to their 

 burden may lead to a complete break-down. Hence, by 

 some system of signalling we do not rightly understand, 

 they can influence the pyloric janitor to keep the gate- 

 way of the stomach closed and thus delay the passage 

 of its contents. Sir Berkeley Moynihan discovered, in 

 connection with disease of the caecum and appendix, that 

 if these parts are inflamed they take control of the pyloric 

 janitor. To the superficial observer of such patients, the 

 stomach seems at fault ; they blame it for holding up its 

 contents, and their first thought may be to force it to 

 work by applying strong medicines, thus bringing about 

 the very condition which Nature is trying to prevent by 

 means of an ingenious mechanism. 



There is also another matter which must be touched 

 on here — one which was skimmed over when speaking of 

 the heart. We saw that the contractions of the ventricles, 



