20 



quantity of strongly acid chyme containing the products of gastric diges- 

 tion of the foodstuffs. The pylorus opens to admit the passage of a few 

 cubic centimetres of chyme at a time, and then closes and remains closed 

 so long as the contents of the duodenum continue to be acid. As soon as 

 the duodenal contents are neutralised, the pylorus opens again and allows 

 the propulsion of a further portion of semi-digested chyme into the 

 duodenum. As we have seen, the effect of this acid chyme is to give rise 

 in the cells of the mucous membrane of the first part of the intestines to 

 secretin which, carried by the blood-vessels to the pancreas, excites a flow 

 of strongly alkaline pancreatic juice. We may take it that ten cubic 

 centimetres of pancreatic juice would suffice to neutralise from 15 to 20 

 cubic centimetres of the acid chyme. Pancreatic juice, however, although 

 it contains many ferments, is dependent for the full display of its digestive 

 activity on the cooperation of the other juices which are poured into the 

 intestines at the same time namely, the bile and the succus entericus. 

 Pancreatic juice contains preformed both a fat-splitting ferment and a 

 starch-splitting ferment. The activity of both these ferments is, however, 

 doubled or trebled if bile be simultaneously present. Moreover, the fat- 

 splitting properties of pancreatic juice are of little avail to the organism 

 unless bile salts are also present, which by their solvent power on fatty 

 acids and soaps and by their effect on surface tension can enable the 

 absorption of the products of fat digestion to take place. It is essential, 

 then, that the secretion of bile shall take place at the same time as, and 

 in proportion to, the flow of pancreatic juice. The simultaneous and 

 correlated flow of these two juices is effected by one and the same 

 mechanism. Bayliss and I observed that if a cannula were introduced into 

 the bile duct, the cystic duct having previously been ligatured, intravenous 

 injection of secretin evoked not only the flow of pancreatic juice but also 

 an increased flow of bile. Most extracts of the mucous membrane of the 

 small intestine contain small traces of bile salts which are themselves 

 cholagogue and might, therefore, be responsible for any increase in bile 

 secretion observed as the result of the injection of ordinary extracts of 

 intestinal mucous membrane. The presence of bile salts in our extracts 

 was, however, guarded against, since, in our experiments on the influence 

 of secretin on bile, we used for the preparation of secretin only mucous 

 membrane, which had been previously thoroughly extracted with boiling 

 absolute alcohol and proved by special experiment to contain no trace of 

 bile salts. 



Still more important for the full display of the powers of the pancreatic 

 juice is the cooperation of the succus entericus. It was shown in Pawlow's 

 laboratory that the proteolytic effects of pancreatic juice obtained from 

 a pancreatic fistula were enormously increased by the addition of a small 

 trace of intestinal juice, and it was concluded that the pancreatic juice 

 contains, besides a small amount of trypsin, a large amount of trypsinogen. 

 This latter " preferment " has no action on proteids. The succus entericus 

 contains another ferment, called by Pawlow enterokinase, which has the 

 power of converting trypsinogen into trypsin. More lately it has been 



