94 PRINCIPLES OF VETERINARY SCIENCE 



the growth of all kinds of bacteria they act as antiseptics, thus 

 preventing excessive fermentation and putrefaction. The per- 

 centage of hydrochloric acid is considerably lower in herbivora 

 than in carnivora, therefore micro-organisms are not so readily 

 destroyed, and have a longer opportunity to act on the sugars 

 resulting from digestion of the carbohydrates. On a diet of 

 starchy food the lactic acid always exceeds the hydrochloric acid, 

 suggesting it may be due, in part at least, to the fermentation of 

 the carbohydrates. 



The rate of emptying the stomach is controlled in a measure 

 by these acids, but not to such an extent as in the dog, for the 

 pylorus of the horse generally is open. Furthermore, while the 

 acidified protein in the stomach causes the pyloric sphincter to 

 relax, in the intestine it causes it to contract and close. Thus 

 an alternate opening and closing of this valve occurs. The 

 semi-fluid material is squirted through the pylorus; in some 

 animals the noise is audible. 



Many chemical theories have been advanced to explain the 

 production of hydrochloric acid. One is based on the fact that 

 during the process of digestion in both the stomach and intes- 

 tines a large amount of C0 2 is formed from fermentation of 

 carbohydrates. This is absorbed 1 into the circulation as is that 

 from tissue oxidation. It is thought that this C0 2 decomposes 

 the NaCl of the blood and produces Na 2 C0 3 and free HC1. The 

 origin of the latter in the stomach is thus accounted for. The 

 sodium carbonate is finally excreted in the urine or goes to form 

 bone. 



Schattke found an acid reaction in all parts of the horse's 

 stomach ninety minutes after feeding; previous to that time the 

 esophageal portion gave an alkaline or neutral reaction due to 

 the saliva. 



Water is secreted by the gastric glands. Its production varies 

 with the dryness of the food. When the stomach ingesta are 

 ready for passage into the intestine they contain a surprisingly 



1 This explanation is not entirely satisfactory as it neither shows why 

 HC1 is not eliminated by the kidneys nor why Na 2 C0 3 is not found in the 

 gastric juice. Furthermore, MeCollum has found that in the bodies of 

 pigs under experimental conditions, decomposition of the sodium chloride 

 molecule and formation of hydrochloric acid does not occur. Therefore 

 it is probable that the process of HC1 production is due to vital action. ' 



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