DIGESTION. 71 



do not extend so wide as the upper, but by the lateral motion of 

 the jaws a grinding process is effected. During the time the 

 food is thus being masticated, an abundant supply of saliva is 

 furnished by the various salivary glands, and the soft bolus is 

 then passed into the gullet by the tongue. By the muscles of 

 the gullet or pharynx the food is passed into the oesophagus, by 

 the muscular coat of which it is forced into the stomach. 



In swallowing liquids a vacuum is formed in the mouth, and 

 the water is thus sucked in, the tongue forming a sort of channel 

 for its passage. In this operation the lips are surrounded with 

 water, and the air carefully excluded. 



When grain forms the diet of the animal, the nippers have very 

 little to do ; they merely collect the food, which is transferred to 

 the molar teeth to be effectually ground. Mastication is, of 

 course, much slower with this food than with grass, otherwise 

 a portion of the food would be swallowed whole, and passed 

 through the body without having its nutritious principle ex- 

 tracted ; a circumstance which often happens with very greedy 

 feeders, and likewise in old horses, from the teeth being im- 

 perfect. We have before remarked that the stomach of the 

 horse is very small in proportion to the size of the animal, for 

 which fact a reason is afforded by the habits and peculiarities of 

 the animal. The ox, we find, has no less than four stomachs : in 

 him the process of digestion is comparatively tedious and slow ; 

 for having filled his paunch, he becomes more sluggish and 

 disinclined for motion ; he lies down, and his food undergoes a 

 second process, that of rumination. 



Carnivorous animals have a capacious stomach, which they 

 ravenously fill with a large quantity of animal food, after which 

 they become sluggish, and lie down and sleep. 



The horse, however, in a natural state, is almost constantly in 

 motion. He eats Avhen he can, and as often as he can, and is 

 almost immediately afterwards prepared for flight. Having a 

 small stomach, it does not, even when filled, press so heavily 

 against the diaphragm as to impede respiration, as with other 

 animals we have mentioned ; and although the practice of work- 

 ing him on a full stomach is by no means to be recommended, yet 

 it is surprising what exertions he is capable of even in this state. 

 Thus a horse, from being furnished with a small stomach, is 

 rendered more useful for purposes of speed, or di'aught, and con- 

 sequently more serviceable to man. 



The food having entered the stomach, is there submitted to 

 the action of a fluid secreted by the villous coat of the stomach, 

 and termed the gastric juice. This fluid is very peculiar in its 

 nature, and has the power of separating the whey from milk. 

 It opei'ates chemically on the food, and converts it into a soft 

 pulpy mass, called chyme, in which state it is pasa,ed into the 



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