DIGESTION 177 



nothing can be forced out by this passage, not even after death 

 or under great pressure. 



The physiological points of interest in the structure of the 

 horse's stomach are : (1) That it is small ; (2) that it is not in 

 contact with the abdominal wall, but rests on the colon ; (3) that 

 the outlet and inlet are situated close together ; (4) that the cardia 

 is tightly constricted ; (5) that only a portion of its surface is 

 capable of secreting a digestive fluid ; (6) that there are remark- 

 able differences in the character and nature of the various regions 

 of its mucous membrane. 



We can now consider the stomach digestion of the two chief 

 foods used for horses — viz., hay and oats. 



Digestion of Hay. — Hay, as has been stated, mixes in the 

 mouth with four times its bulk of saliva, and after a very perfect 

 grinding passes into the stomach. If the stomach be empty it is 

 of no size, and the material lies in the lesser curvature and pyloric 

 region ; as the viscus gradually fills, the greater curvature is 

 occupied, the gastric juice begins to act, and chyme commences 

 to pass into the intestines probably in a very imperfectly elabor- 

 ated form. Assuming the animal to have finished eating hay, 

 we now find the output into the intestine becomes small and slow. 

 The gastric juice has an opportunity of acting more thoroughly 

 upon the ingesta, which turn yellow on that surface which is in 

 contact with the villous wall, the compression of the stomach on 

 the contents causing them to become distinctly moulded into a 

 mass the shape of the viscus. Owing to gravity there is more 

 fluid towards the pylorus than elsewhere, and for the same reason 

 the greater curvature in all probability is fuller than the lesser. 

 The material in the stomach is perfectly comminuted, resembles 

 firm green and yellow faeces, and the smell is peculiar, like sour 

 tobacco. The yellowness is due to the gastric juice, and is con- 

 sequently more marked towards the pylorus ; the portion coloured 

 green is the part as yet unacted upon by the juice. The entire 

 surface of the stomach and its contents are now acid, excepting at 

 the cardia, where it may occasionally be alkaline from swallowed 

 saliva ; the acidity is greater at the fundus than at the cardia. 

 This general acidity shows that a diffusion of the gastric juice 

 must have been going on. There is no evidence of any churning 

 motion ; the cake-like condition into which the hay is compressed 

 is produced by the simple compression of the stomach walls. 



The duration of hay-digestion in the stomach is very variable. 

 In examining a series of digestions hour by hour, such as will 

 be mentioned presently, moderately uniform results may be 

 obtained, but even these are sure to be here and there broken by 

 excessive, or conversely by very small, digestions which cannot 

 be explained. 



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