200 A MANUAL OF VETERINARY PHYSIOLOGY 



lactic acid is present in the former, and both lactic and hydro- 

 chloric acid in the latter. In the fourth stage starch conversion 

 is nearly complete, while hydrochloric acid predominates in all 

 the regions, and protein conversion is general. 



Stomach Digestion in the Dog. 



Very complete knowledge of the physiology of the dog's 

 stomach exists, for nearly all the work carried out to elucidate 

 the physiology of the human stomach has been effected on the 

 dog, and has, to some extent, already been embodied in the 

 previous pages in dealing with gastric juice. 



In the stomach of the dog and cat digestion occurs mainly in 

 the pyloric dilatation or antrum, which is from time to time cut 

 off from the rest of the stomach by the pyloric ring or transverse 

 band (not to be confused with the pyloric sphincter) , so that the 

 general body of the stomach acts mainly as a receptacle, passes, 

 from time to time, material into the antrum for chyme con- 

 version, and then ejects it into the intestines. The length of 

 time material lies in the stomach depends upon its nature and 

 consistence ; both carbohydrates and fats escape into the intes- 

 tines more readily than protein, and this appears to depend 

 upon the strength of acid present. A weaker acid sufficing for 

 non-protein food is more rapidly neutralised in the small intes- 

 tines, and the opening of the pylorus appears to depend upon 

 impulses passing from the duodenum as soon as the last received 

 acid supply has been neutralised in that bowel. 



A flesh diet requires very little saliva and practically no masti- 

 cation, but its digestion is slow, in spite of the fact that it is 

 taken in a form closely allied to that in which it is assimilated. 

 Colin states that it takes a dog twelve hours to digest an amount 

 of meat which it could eat at one meal. The substances most 

 difficult of digestion are tendons and ligaments, but their digestion 

 is facilitated by boiling; liver and flesh are best given raw, as 

 cooking interferes with their digestibility. The gastric juice of 

 the dog is fully described at p. 187. 



Absorption from the Stomach. — The needful changes having 

 occurred in the stomach — and we now refer principally to the 

 stomach of the horse — the next step is to inquire into the pro- 

 portion of food so altered as to be rendered fit for absorption. 



Experiment shows that in the stomach 40 to 50 per cent, 

 of the carbohydrates have been converted into sugar, whilst 

 40 to 70 per cent, of the proteins are converted into peptones. 

 When food has been long in the stomach, not more than 10 per 

 cent, of the proteins escape being peptonised. In ruminants 



