THE JUICES POURED OUT UPON THE FOOD. 77 



has not as yet been entirely established. It is the name 

 given by PAWLOW to a substance, discovered by CHEPO- 

 WALNIKOW in the mucous membrane and secretions of the 

 small intestine, which has the power of converting the 

 inactive preferment of the pancreas into the active alkali- 

 pro teinase (trypsin). HAMBURGER and HEKMA have found 

 this substance in human intestinal juice. 



Pancreatic Secretin is in no sense a ferment. It is a term 

 applied by BAYLISS and STARLING to a substance formed in the 

 upper portion of the intestine during digestion, which is 

 absorbed into the blood and, reaching the pancreas, increases 

 the secretion from this gland. 1 



The secretion of the large intestine has been studied in the 

 human being in cases of fistula opening into the ascending, 

 transverse, or descending portions of this part of the intestinal 

 tract, and in animals in which artificial fistulse have been 

 created. The observations of all who have worked on the 

 secretion of the large intestine agree in stating that it is small 

 in amount and mainly composed of mucus. The juice is 

 alkaline in reaction and seems to contain no enzymes of 

 digestive importance. It is probable, however, that the food 

 which escapes through the ileocsecal valve, mixed with the 

 enzymes poured out upon it higher up in the alimentary canal, 

 continues to undergo digestive change in the large bowel. Of 

 greatest importance is the absorption which occurs in the 

 various portions of the colon. While the food is soft in con- 

 sistency in the ascending portion of the large intestine, it 

 becomes less liquid and finally firm as the transverse and 

 descending portions are reached, until in the rectum the solid 

 faeces are formed. 



While no enzymes derived from the large intestine itself act 

 upon the food in the colon, enzymes derived from the bacteria 

 present here bring about most profound changes in the food. 



1 The ferments are considered in greater detail in the succeeding 

 chapters. Enterokinase is discussed in Chapter XIII, Part 4, pan- 

 creatic secretin in Chapter XII, Part 5. 



