DIGESTION 247 



take place quite efficiently when no gastric juice is 

 secreted at all, as in cases of achylia. Probably the 

 mere presence of food is in itself an exciter of the 

 movements. There is equal doubt as to the agent 

 which unlocks the pylorus and allows the food to escape 

 into the intestine. According to some, free HC1 is also 

 the active agent in this process. This, however, is un- 

 likely for several reasons. In the first place, as has just 

 been pointed out, the discharge of the stomach contents 

 into the intestine may take place quite quickly when no 

 free HC1 is present at all. In the second place, observa- 

 tions on patients with gastric fistula show that free HC1 

 tends to inhibit the opening of the pylorus rather than 

 to favour it,* and there is some clinical evidence for the 

 belief that the presence of an excess of acid may cause 

 pyloric spasm. In the third place, there is no doubt 

 that the presence of acid in the duodenum prevents the 

 pylorus from opening until it has been neutralized. It 

 would be very unlikely, surely, that the presence of acid 

 on one side of the pylorus should open it, and on the 

 other should cause it to close. On the whole it seems 

 more probable that the pylorus opens when the waves of 

 contraction in the stomach become strong enough, pro- 

 vided it be not reflexly inhibited by distension of the 

 duodenum or the presence in the latter of an acid 

 reaction or of fat. Warmth, internal or external, and 

 the presence of alkalies in the stomach seem to unlock 

 the pylorus; hence, probably, the usefulness of poultices, 

 hot liquids, and alkalies in relieving gastric pain. On 



* See v. Pfungen, Centralb. /. Physiol, 1S87-88, i. 220, 

 277. 



