DIGESTION 343 



is also rendered innocuous by trypsin. Erepsin, however, is 

 not specific to the secreted intestinal juice, for it occurs also, not 

 only in the mucous membrane of the intestine, which, indeed, 

 contains a greater quantity of it than the succus entericus, 

 but in all animal tissues hitherto investigated. The kidney in 

 mammals is even richer in erepsin than the intestinal mucous 

 membrane. Next to these come the pancreas, spleen, and liver, 

 then at a long interval the heart muscle, while skeletal muscle 

 and brain-tissue are poorest of all in the ferment. The intestinal 

 mucosa varies in its erepsin content at different levels and on 

 different diets. In cats on a meat or a mixed diet the duo- 

 denum is about five times richer in the ferment than the stomach. 

 The ileum is about half as rich as the duodenum, and the jejunum 

 occupies an intermediate position between the duodenum and 

 ileum (Vernon). The secretion of Brunner's glands in the duo- 

 denum, which resemble in structure the pyloric glands of the 

 stomach, digests coagulated albumin, although its proteolytic 

 powers are feebler than those of the pancreatic juice. 



The most characteristic constituent of succus entericus is a 

 ferment, enterokinase, which differs from all the ferments we 

 have hitherto described in acting not directly upon the food- 

 stuffs, but upon the trypsinogen of the pancreatic juice, changing 

 it into the active enzyme trypsin. It may therefore be spoken 

 of as a ferment of ferments. It has been previously stated that 

 freshly secreted pancreatic juice is without action upon proteins. 

 The addition of succus entericus immediately confers upon it a 

 high degree of proteolytic power. In one experiment pancreatic 

 juice, obtained by a temporary fistula, required four to six hours 

 to dissolve fibrin, and did not attack coagulated albumin even in 

 ten hours. On addition of succus entericus, the same pancreatic 

 juice dissolved fibrin in three to seven minutes, and rapidly 

 digested coagulated albumin (Pawlow). In like manner a 

 glycerin extract of a fresh pancreas has hardly any effect on 

 proteins ; a similar extract of a stale pancreas is active. The 

 fresh pancreas contains trypsinogen, which is soluble in glycerin, 

 for the inert extract becomes active when it is treated with dilute 

 acetic acid, or even when it is diluted with water and kept at 

 the body-temperature. If the fresh pancreas be first treated with 

 dilute acetic acid, and then with glycerin, the extract is at once 

 active. The trypsinogen can therefore be activated within the 

 pancreatic cells, gradually when the pancreas is simply allowed to 

 stand after excision, more rapidly in presence of the dilute acid. 

 The ordinary tests for ferment action (destruction by boiling, 

 activity in very small amounts, etc.) have shown that this pro- 

 perty of the intestinal juice is due to a ferment, although it 

 differs in certain respects from most ferments for instance, in 



