DIGESTION IN THE LAJRGE INTESTINE. 423 



contents is usually strongly alkaline, and we have then to deal -with 

 processes which are evidently putrefactive in nature. But a small 

 portion of the nutritive parts of food will, however, be subjected to 

 these changes, since probably digestion, especial^ in carnivora and 

 ruminants, is completed before this portion of the tract is reached. 

 Indol and phenol are here found, and result from the putrefactive changes 

 in albuminoids, while lactic acid, butj-ric acid, acetic acid, carbonic acid, 

 and hydrogen are met with and result from changes in carbohydrates. 

 The different gases found in the small intestine have been already men- 

 tioned ; their character and amounts vary according to the nature of the 

 diet. 



The following table represents their relative amount from different 

 diets in dogs : — 





C0 2 . 



N. 



H. 



0. 



Meat diet, 



. 40.1 



45.5 



13.9 



0.5 



Bread diet, 



. 38.8 



54.2 



6.3 



0.7 



Vegetable diet, 



. 47.3 



4.0 



48.7 





X. DIGESTION IN THE LARGE INTESTINE. 



The absorption of all the alimentary elements which are essential to 

 nutrition is in the carnivora achieved in the small intestine. In these 

 animals the caecum is absent or rudimentary, and the colon is short and 

 apparently uncomplicated; but in the immense caecum of solipedes and 

 certain other herbivora the digestive process goes on, and the changes 

 which the food undergoes in this part of the alimentary tract now 

 deserve attention. 



1. The Functions of the Caecum. — The caecum, or blind gut, is that 

 portion of the large intestine which usually occurs as a diverticulum at 

 the point of junction of the small and large intestines, and in which the 

 contents of the former empty. In man and carnivora this reservoir is 

 rudimentary, and receives the alimentary mass after all its nutritive 

 properties have been extracted. In this class of animals, therefore, 

 the caecum can have no physiological function to fulfill. In reptiles, 

 batrachians, and the fish the small intestine is directly continuous with 

 the large intestine, scarcely increasing in diameter, and no caecal append- 

 age is present, the reservoir only being represented by a long, lateral 

 dilatation. It is only in mammals and in birds that one or two pouches 

 are found at the point of union of the small and large intestines, and 

 which furnish a new reservoir to the alimentary matters before permitting 

 them to enter into the large intestine to be finally expelled. 



In birds, the caecum varies in development and importance according 

 to their normal diet. In the flesh-eating birds, the stomach and small 

 intestine are amply sufficient to produce the necessary chemical trans- 

 formations in the food to render it capable of being absorbed. Their 



