GASTRIC DIGESTION. 339 



The capacity of the stomach is, of course, very variable in different 

 animals in proportion to their size. It is very considerable in the car- 

 nivora ; thus the dog's stomach maj' contain from two to ten litres ; in 

 the hog seven to eight litres will represent the average capacity ; while 

 in the horse, in proportion to its size, it is relatively very much smaller, 

 the capacity of the stomach of the horse varying from sixteen to 

 eighteen litres, or only one-tenth or one-twelfth of that of the intestines. 



In the ruminant the mean capacity is stated by Colin to be two 

 hundred and ninety litres. It must be remembered, however, that in the 

 latter case the stomach of the ruminant is never empt} 7 , no matter what 

 may be the duration of abstinence. Thus, Colin found sixty-five kilos 

 of dry food in the first three compartments of the stomach of a cow 

 which had fasted for a very long time; in another, after four clays' 

 abstinence, forty-two kilos were found, while in a third sixtj^-six kilos 

 were found after a fast of two days. 



In the horse, as the stomach fills up with food, the constriction 

 between the right and left halves of this organ disappears, and the stom- 

 ach then takes the shape as seen when distended by air after death. In 

 the horse, no matter how much distended, the stomach is never in contact 

 with the inferior abdominal walls, but is always separated from them by 

 the infra-sternal curvature of the colon and a portion of the gastro-dia- 

 phragmatic curvature. In carnivora the stomach is in contact with the 

 lumbar region above, and with the abdominal walls in the epigastrium 

 and hypochondrium. As the stomach becomes expanded with food, the 

 cardiac and the pjloric sphincters become contracted, and the alimen- 

 tarj- matters by contact provoke contraction of the muscular walls of 

 the stomach, and so serve to mix up the food. 



When the food first enters the stomach these movements are slight, 

 but they gradually become more and more vigorous, and cause a sort of 

 churning motion in the stomach, the food travelling from the cardiac 

 orifice along the greater curvature to the pylorus and returning by the 

 lesser curvature. At the pylorus the circular muscular fibres are the 

 seat of slow, rhythmical contractions, which serve to assist in the pas- 

 sage of the contents of the stomach into the small intestine. While 

 these movements seem to be started by the contact of the food with the 

 mucous membrane of the stomach, it is evidently not a mere mechanical 

 stimulation which produces them, since, when the stomach is fullest, and 

 when, therefore, this mechanical stimulation must be at its height, the 

 movements are the slightest, and become more vigorous as the stomach 

 empties itself. Apparently these contractions are started up by the 

 commencing acidity of the gastric contents, which, at first alkaline, 

 become gradually more and more acid as digestion progresses, coinciding 

 with the increase in vigor of the muscular movements of the walls of 



