GASTRIC DIGESTION 143 



which are ingested without sufficient mastication ("bolted") 1 and which 

 consequently, at times, pass into the intestine in rather large pieces 

 (see Chapter XIV on Feces). 



Gastric rennin, the second enzyme of the gastric juice, is what is 

 known as a milk curdling or protein coagulating enzyme. Rennin acts 

 upon the casein of the milk, splitting it into a peptone-like body and 

 soluble paracasein. This soluble body, in the presence of calcium 

 salts, combines with calcium, forming calcium paracasein which is 

 insoluble and precipitates. There is some uncertainty regarding 

 the reaction to litmus in which gastric rennin shows the greatest 

 activity. It is, however, said to be active in neutral, alkaline, or acid 

 solution. However, it probably possesses its greatest activity in the 

 presence of a slight acid reaction, as would naturally be expected. It 

 is especially abundant in the gastric mucosa of the calf, and is used 

 to curdle the milk used in cheese making. Gastric rennin is always 

 present normally in the gastric juice, but in certain pathological con- 

 ditions such as atrophy of the mucosa, chronic catarrh of the stomach, 

 or in carcinoma it may be absent. 



The theory that the proteolytic activity and the milk curdling prop- 

 erty of the gastric juice reside in a single substance is causing much 

 controversy at the present time. The theory was originally advanced 

 by the Pawlow school. 2 According to Nencki and Sieber, 3 the milk 

 curdling and protein hydrolyzing activities reside in definite and distinct 

 side chains of a single mammoth molecule. The view which has rather 

 the strongest support, however, is to the effect that there are two entirely 

 distinct enzymes. Important evidence has been advanced in favor of 

 this view by Hammarsten, 4 Taylor, 5 and Hemmeter. 6 Burge 7 has re- 

 ported experiments upon the influence of a direct electric current upon 

 solutions possessing typical rennin and peptic activities. By this 

 means he was able to prepare a solution possessing strong rennin 

 activity but entirely devoid of peptic activity. This furnishes strong 

 evidence against the identity of the two enzymes but does not neces- 

 sarily deny the accuracy of the side-chain theory. 



Gastric lipase, the third enzyme of the gastric juice, is a fat-splitting 

 enzyme. It possesses but slight activity when the gastric juice is of 

 normal acidity, but evinces its action principally at such times as a 



1 Foster and Hawk: Proceedings of the Eighth International Congress of Applied Chem- 

 istry, New York, September, 1912. 



2 Pawlow and Parastschuk: ZeitschriftfurPhysiologische Chemie, 42, 415, 1904. 



3 Nencki and Sieber: Zeitschr ift fur Physiologische Chemie, 23, 191, 1901. 



4 Hammarsten : ZeitschriftfurPhysiologische Chemie, 56, 18, 1908; 94, 291, 1915. 

 6 Taylor: Journal of Biological Chemistry, 5, 399, 1909. 



6 Hemmeter: Berliner klinische Wochenschrift, Ewald Festnummer, 44, 1905. 



7 Burge: American Journal of Physiology , 29, 1912. 



