Digestion. 127 



of knowing ; all we know is that it is less during hunger than 

 during digestion, and is less in ruminants than in horses. 



We have no knowledge of the nerves governing the 

 secretion of gastric juice. 



The action of the gastric juice is directed solely against 

 the proteid principles of the food. There are other changes, 

 no doubt, besides peptonizing occurring in the stomach, 

 but these are independent of the gastric juice, and are 

 perhaps, in some cases, inhibited by it. 



Gastric juice converts albumins into Peptones. This 

 change occurs whether an animal or vegetable proteid be 

 given. The conversion is not a direct one, as between 

 albumins and peptones occur the intermediate products 

 albumoses. 



It is well known that albumins cannot pass through an 

 animal membrane, whereas the distinctive character of 

 peptones is their power of dialysing, which enables them, 

 no doubt, to pass readily into the absorbent vessels of the 

 intestines. 



The amount of peptone at first produced is small; 

 especially is this the case early in digestion, for, as we shall 

 presently show, according to Ellenberger, peptic digestion is 

 the second stage of stomach digestion in the horse. 



The amount of peptone in the stomach is stated by the 

 same observer to be smaller in the left half of the stomach 

 than in the right ; according to my experience peptone 

 disappears as soon as it is formed, for I have never suc- 

 ceeded in finding any in the stomach of the horse. 



But the gastric changes are not quite so simple as would 

 at first sight appear. Experimental inquiry shows that 

 peptones are obtained in two forms, one remaining stable 

 and undergoing no further change, whilst the other may, 

 under the influence of one of the ferments of the pancreatic 

 juice (trypsin), be split up into leucin and tyrosin, two 

 amido acids which will engage our attention later on. 



All peptones which yield as further products leucin and 

 tyrosin are termed hemi-peptones, whilst those which do not 

 are called anti-peptones. 



