192 A MANUAL OF VETERINARY PHYSIOLOGY 



Pawlow believes that the quantity and quality of the gastric 

 juice will be found to depend on the character of the food, so 

 that while in some cases an economical production is obtained, 

 in others a stronger or weaker fluid is poured out, depending upon 

 the work to be done, the regulation of which is probably a specific 

 action on the part of the food itself. 



In a meal of meat, bread, and milk, taken separately, each 

 article of diet produces not only a definite rate of secretion of 

 gastric juice, but also an alteration in the quality of the ferment 

 suited to the work it has to perform. Thus flesh or bread cause 

 a maximum secretion during the first hour of digestion ; milk 

 during the second or third hour. The greatest digestive powers 

 of the gastric juice are found to occur with a meat diet, while 

 the weakest proteolytic action occurs with milk. 



If an animal fed for weeks on a bread-and-milk diet be sud- 

 denly placed on meat, the power of dealing with protein is at 

 first weak ; the juice is in sympathy with a starchy rather than 

 a protein diet. If another change be made when the meat diet 

 is being satisfactorily dealt with, and the animal put back on 

 bread and milk, the whole process has to be reversed, and the 

 glands this time brought into tune with a starchy rather than 

 a protein diet. 



It is true this observation has been made on the pancreatic 

 juice, but what holds true for it cannot be doubted as being true 

 for other digestive secretions. Further, we have the overwhelm- 

 ing proof of everyday management of horses that sudden changes 

 in diet are productive of disease. Whether the above facts 

 regarding digestive juices and changes in diet are explained by 

 what we know of the function of chemical excitants — ' hormones ' 

 — remains to be proved. 



Such is the modern aspect of stomach digestion. We appear 

 to have approached appreciably nearer to a better understanding 

 of the circumstances attendihg digestive troubles in the horse, 

 and, as we shall have to point out again in dealing with pan- 

 creatic secretion, Pawlow's work explains why a sudden change 

 of a long-continued diet is bad, and as we know, is followed in 

 horses by disastrous consequences. 



Starch Conversion. — There are other changes occurring in the 

 stomach independently of peptonising or of gastric juice. If a 

 horse be fed on oats and the stomach fluid examined, it will be 

 found to contain an abundance of sugar. The sugar is produced 

 from the starch of the grain, and is not, according to our observa- 

 tions, the result of the action of saliva. Abundant saliva exists 

 in the stomach, but it will be remembered that in the horse we 

 have never succeeded in getting it to give any evidence of starch 

 conversion. The question, therefore, is, W T hat is the cause of 



