FUNCTIONS OF THE LARGE INTESTINE. 183 



meat diet, and is then useful as a means of preventing the inju- 

 rious effects of too great proteid absorption. 



The gastric chyme is therefore completely changed in the duo- 

 denum, and in the other parts of the small intestines we find in 

 its stead a thin creamy fluid which clings to the mucous membrane, 

 coats over its folds (valvulse conniventes) and surrounds the long 

 villi of the jejunum, etc. This intestinal chyme is the form in 

 which the food is presented to the mucous membrane for absorp- 

 tion. It resembles somewhat by its whiteness the fluid called 

 chyle which flows in the lacteals, and formerly was considered to 

 be identical with it. This creamy lining is the chief material 

 found in the upper part of the small intestine, the coarser parts 

 of the food being hurried on by peristaltic action to the large in- 

 testine. 



In the large intestine the secretion of the long closely-set Lie- 

 berkiihn's follicles is the only one of importance. Its reaction 

 and that of the mucous membrane is alkaline, but the contents of 

 the colon are acid owing to certain fermentative changes which go 

 on in this part of the intestine. 



Of the changes brought about in the large intestine by the 

 agency of the digestive juices we know but little. Judging from 

 the large size of the caecum and colon in herbivorous animals, we 

 are prompted to conclude that vegetable substances, possibly cel- 

 lulose, may be dissolved here, but we do not know how this is 

 accomplished. Although devoid of villi, the large intestine can 

 certainly absorb readily such materials as are in solution. As 

 the insoluble materials pass along the small intestines the supply 

 of fluid is kept up to about the same standard, the absorption and 

 secretion being about equal ; but in the large intestine, the absorp- 

 tion of the fluid so exceeds the secretion in amount that the undi- 

 gested materials are gradually deprived of their fluid, and are 

 converted into soft solid masses which pass on to be added to the 

 faeces. 



Owing to its absorbent power the large intestine is a ready and 

 rapid channel by which materials can be introduced into the 

 system in cases in which the stomach is too irritable to retain food. 



The quantity of faeces evacuated in the day depends upon the 



