DIGESTION 173 



impossible to establish a gastric fistula in this animal owing to 

 the distance the stomach lies from the abdominal wall ; pure 

 gastric juice has, therefore, never been obtained from the horse. 



The first peculiarity to be noticed in soliped digestion is that 

 the stomach is rarely empty ; it is only when horses have purposely 

 been deprived of food for not less than twenty-four hours that an 

 empty stomach can be obtained. On the other hand, feeding 

 experiments show that very shortly after food arrives in the 

 stomach it commences to pass out, and the difficulty thus 

 presented to the observer in reconciling these opposed facts is at 

 first sight considerable. It is perfectly true that food does pass 

 out early, it is equally true that it is long retained, these opposite 

 conditions being the result of the periods of digestion. When 

 food enters an empty stomach, it passes towards the pylorus, 

 where it meets with a fluid of an alkaline or neutral reaction 

 which has come from the mouth. As more food is consumed an 

 acid fluid is secreted in the stomach, and material commences 

 to pass out at the pylorus into the bowel, the amount passing out 

 not equalling at present the amount passing in. Thus the 

 stomach becomes gradually distended, and when two-thirds full, 

 which is the condition in which the most active digestion occurs, 

 the amount passing out will, if more food be taken, equal the 

 amount being swallowed, so that we have a stream of partly 

 peptonised chyme streaming out of the right extremity, while a 

 corresponding bulk of ingesta is entering the inert left sac. In 

 fact, the stomach may during feeding allow two or three times 

 the bulk of food to pass out which remains in it when the meal is 

 finished. No sooner is the feed finished than the passage of 

 chyme into the duodenum ceases, or becomes so slowed down 

 that only small quantities of food pass out, and so gradually 

 does this occur that it will be many hours before the stomach 

 is really empty, though had the process continued as it com- 

 menced, it would not have contained anything at the end of an 

 hour. This condition of stomach digestion in the horse may be 

 variously modified, depending on the nature of the food, the 

 quantity given, the form in which it is given, the order in which 

 one food follows another, and whether water be given before or 

 after feeding. All these are points requiring our attention, but 

 before giving it we must briefly look at the stomach itself. 



The mean capacity of a horse's stomach is, according to Colin, 

 from 15 to 18 litres (3 to 4 gallons) ; these figures were obtained 

 from a very large number of observations, and give the extreme 

 size of the organ when distended. The viscus is under the best 

 physiological conditions for digestion when it contains about 

 10 to 12 litres (2 to 2*5 gallons), or is distended to two-thirds of 

 its capacity. The mucous membrane of the stomach of the 



