CHAP. II.] ITS PHYSIOLOGY, — GASTRIC JUICE. 133 



the horse's stomach by what is termed "trituration," 

 or pounding ; but, upon reference to the figure 

 which illustrates another organ, (at page 158.) the 

 reader will be able to form a more accurate notion, 

 near enough for his purpose, how the stomach con- 

 tracts its sensible part upon its contents. This 

 sensible coat secretes a juice which, from its strong 

 gastric nature, not only digests the food, but would 

 also corrode the stomach itself (insensible though it 

 be), were it not supplied with another fluid for its 

 protection, in the saliva or spittle that descends the 

 gullet along with the food. This saliva is also 

 secreted, in some measure, when the animal may 

 not be feeding : but, whenever this supply fails, the 

 gastric juice predominates so much, as to cause a 

 galling pain in the stomach, and occasion in the 

 animal a ravenous desire for filling it, if not with 

 food, at least with some substance that may keep 

 it distended, and perhaps carry off the painful 

 superabundance. Horses so circumstanced, when 

 in harness, gnaw the pole or shaft, or bite at each 

 other, and soon learn to become crib-biters, gnaw- 

 ing any thing they can come near, as well as the 

 manger ; litter, bits of old wall, and dirt, at length, 

 are found by them agreeable to their palate. See 

 further at section 49. 



The insensible membrane we spoke of, by its 

 loose folds, forms, at the entrance of the stomach, 

 a kind of valve, which prevents regurgitation of the 

 food, like that of ruminating animals ; and a simi- 

 lar contrivance at its termination in the lower or 



