358 COMPARATIVE PHYSIOLOGY. 



tion is unusually active, as is well seen in the dog ; if the stom- 

 ach is capacious the intestine is shorter, also exemplified in 

 this group. The stomach may be small and the small intes- 

 tines not lengthy, but the large intestine of enormous size, as in 

 the horse. 



When the quantity of starchy matters found in the food of 

 the animal is large, provision is made for its digestion in sev- 

 eral parts of the alimentary tract. This is seen in the horse 

 and other herbivora. Mastication is fairly complete in these 

 animals, yet a part of the small stomach of the horse is a sort 

 of oesophageal dilatation (Fig. 266) in which amylolytic diges- 

 tion goes on by the action of the swallowed saliva and possibly 

 by a ferment provided in this region of the organ. 



The gastric juice of the horse has been proved capable of 

 digesting starch, possibly because mixed with the swallowed 

 saliva. The stomach of the pig is large, and both proteid and 

 starchy digestion exceedingly active. In the intestines the pro- 

 cesses are of brief duration, but very effective. 



Digestion in the upper part of the small intestines is, in 

 some animals, as the horse, really a continuation of that in the 

 stomach ; or, at all events, the contents of the duodenum and 

 jejunum are usually acid in reaction, so that the digestion 

 peculiar to one region of the tract does not always abruptly 

 end when food has left that part. The readiness with which 

 food passes from the stomach into the intestines is very vari- 

 able in different animals, and even in the same animal under 

 different circumstances. In the horse the pyloric orifi.ce seems 

 never to be very tightly closed, though in most of our domestic 

 animals the reverse is the case ; and with them the quantity of 

 u'hdigested material, as fat, that passes into the small intestine 

 depends on the rate of digestion and absorption in the latter. 



In the horse, if water, or even hay, be given after oats a por- 

 tion of the latter is soon carried on into the intestines, so that 

 the obvious rule for feeding such an animal is to give the water 

 and hay before the oats, or, at least, the water and no hay im- 

 mediately after the oats. 



Digestion in the large intestine is of great importance in the 

 monogastric herbivora, as the horse. The caecum is of enor- 

 mous size — about twice that of the stomach — and has communi- 

 cation with the colon by a small opening, so that it furnishes a 

 sort of supplementary reservoir for digestion as well as for 

 water. As the results of experiments, it has been concluded 



