994 DIGESTION 



(a) It is Antiseptic. Whenever carbohydrates are ingested, a certain number 

 of micro-organisms are also taken in. These give rise to fermentations, in the 

 course of which considerable quantities of lactic acid may be produced. The 

 subsequent outpouring of hydrochloric acid destroys many of these organisms, 

 as well as others of pathogenic character, but some of them always escape into the 

 intestine (bac. acidi lactici), where they find a more suitable medium for their 

 growth. 



(b) It Inverts Sucrose into Glucose and Fructose. This action is not due to the 

 presence of an invertase in this juice, but to the hydrochloric acid and such invert- 

 ing enzymes as may be present in the food ingested. 1 



(c) It contains a fat-splitting enzyme or lipase. Its action in this regard is two- 

 fold, because the hydrochloric-pepsin combination dissolves the protein constitu- 

 ents and investments of the fat-cells, and allows the fat to escape and to coalesce. 

 In addition, a small quantity of lipase is present which splits the emulsified fat 

 into glycerol and fatty acids, but naturally, the hydrolysis going on in this organ 

 is insignificant when compared with that effected in the intestine by the pan- 

 creatic juice. The origin of this lipase is somewhat in doubt; some claim that 

 it is regurgitated with the contents of the small intestine and some, that it is an 

 actual product of the gastric mucosa. It is of much greater importance to the 

 suckling than to the adult. 



(d) It Curdles Milk. This property of gastric juice is due to its ferment 

 rennin or chymosin 2 which, as has been mentioned above, appears to be formed 

 separately from, the pepsin. 3 It initiates a two-fold process, namely, theconversion 

 of caseinogen into casein, and the combination of the altered casein with the 

 soluble calcium salts to form a curd. 4 This action is greatly accelerated by the 

 hydrochloric acid which in itself is capable of precipitating caseinogen, but this acid 

 is by no means an indispensable factor as is provided by the fact that the curdling of 

 milk also takes place in a neutral or alkaline medium, but not after the milk has 

 been boiled. Moreover, the curd produced by rennin in the presence of calcium 

 salts, exhibits certain properties which are quite different from those exhibited by 

 the acid precipitate. At all events, the newly formed casein is subjected later on 

 to the action of pepsin in the same way 'as other proteins. It seems, however, 

 that the curdling of milk takes place before much acid has been secreted; in fact, 

 milk is not an effective stimulant for the secretion of hydrochloric acid, and is used, 

 therefore, to allay hyperchlorhydria. To the suckling, the curd is of profound 

 importance, because it tends to retain this important nutritive material for a longer 

 time in the stomach so that it may undergo thorough digestion. 5 



(e) It contains a proteolytic enzyme. This is its most important property. The 

 combination of pepsin and hydrochloric acid converts the proteins of the food into 

 peptones, but does not change their constituent polypeptides into their ultimate 

 cleavage products, the amino-acids. This .change is effected by hydrolysis, the 

 first stage being the formation of acid meta-protein, and the next step, the forma- 

 tion of proteoses, such as albumoses, globuloses, vitelloses, etc., as follows: 



Protein 



Acid meta-protein 



( p . | Proteo-proteose 



Propeptone or proteose \ Hetero-proteose 



[ Secondary, Deutero-proteose 

 Peptone or polypeptides 



1 Widdicombe, Jour, of Physiol., xxviii, 1902, 175. 



2 Hammersten, Maly's Jahresb., 1872. 



3 Porter, Jour, of Physiol., xlii, 1911, 389. 



4 Van Slyke, New York Med. Jour., 1909, Proc., Soc. Exp. Biol. and Med., 

 1911. 



8 Gmelin, Pfliiger's Archiv, ciii, 1904, 618. 



