DIGESTION IN THE STOMACH. 67 



amount of blood serum becomes digested much further in a 

 given time by a given amount of trypsin if it receives a prelim- 

 inary digestion by means of pepsin, than when it is acted on by 

 trypsin alone, and erepsin will cause no digestion at all unless 

 the native protein is first of all acted on either by pepsin or 

 trypsin. But peptic digestion is not essential for life, for sev- 

 eral cases are now on record in which individuals have thrived 

 after the stomach has been removed. 



The milk curdling action of gastric juice is due partly to the 

 hydrochloric acid and partly to pepsin. Curiously enough the 

 curdled milk undergoes little further change until the food has 

 got to the small intestine. 



The lipase in gastric juice can act only on emulsified fat and 

 in neutral or alkaline reaction. Fat digestion cannot therefore 

 be an important gastric process. 



It has been supposed that there is a certain specific adaptation 

 between the chemical nature of the food and the amount and 

 strength of the gastric secretion. For example, it has been 

 found, by observations on the juice flowing from a miniature 

 stomach, that feeding in the ordinary way with bread causes a 

 maximal secretion during the first hour, whereas with an equiva- 

 lent amount of flesh the maximum occurs during the first and 

 second hours, and with milk it is delayed till the third or fourth. 

 In proteolytic power the bread juice is much the strongest of the 

 three, but it contains a lower percentage of acid than the others. 



The Movements of the Stomach. Solid food after being 

 swallowed accumulates in the body of the stomach, where on ac- 

 count of an absence of movements it is not uniformly acted on 

 by the gastric juice, its outer layers only becoming digested. In 

 the case of the man, however, some of the food, because of its 

 semi-fluid nature, passes beyond the so-called transverse band 

 and into the pyloric region, in which waves of contraction make 

 their appearance. Starting very faintly at this point, these 

 waves travel towards the pylorus and become gradually more 

 marked until they may become so deep as practically to cut off a 

 portion of the pyloric region from the rest of the stomach. This 

 last portion of the pylorus, sometimes called the pyloric canal. 



