194 DIGESTION 



deed, as yet much in doubt, and here, as elsewhere, hypothesis is a poor 

 substitute for facts. Milk is curdled also by an excess of acid, but that 

 its normal coagulation is not due to the acid of the stomach, but to the 

 rennin's activity, is readily presumed by the fact that neutral rennin 

 promptly coagulates alkaline milk, no acid being concerned at any time, 

 while rennin always is present in the human stomach from birth onward 

 (Heintz). Bacteria cause the curdling of milk after a time, but indi- 

 rectly, by, bringing about the presence of lactic acid, which curdles the 

 milk. (The peptic digestion of casein produces paranuclein, which 

 gradually dissolves.) 



Lipase (steapsin) has been found in the human stomach by Volhard. 

 Aside from the fact that it acts only on emulsified fats (e. g., that of milk), 

 little is as yet known about its work in this organ. 



Hydrochloric acid as found in the stomach undoubtedly exerts some 

 slight hydrolyzing action on the disaccharides (cane-sugar, lactose, and 

 maltose), bringing about thus their " inversion." A special enzyme 

 exists in the succus entericus (page 207), for this purpose, called 

 invertase, and most of the maltose, made by the hydrolysis of carbo- 

 hydrates, is doubtless inverted through the agency of this ferment and 

 not by acid. Lehmann found invert-sugar in the stomach of rabbits 

 fed on beets, while Seegen invariably obtained it from the stomachs of 

 dogs fed on saccharose. No enzyme with an inverting power has been 

 found in the stomach. 



C 12 H 2 A, + H 8 = 2(C 6 H 12 6 ) 



Maltose. Water. Dextrose. 



It is as dextrose that most of the hydrolyzed carbohydrate is absorbed 

 through into the capillaries of the intestinal villi. This hydrolytic in- 

 version performed in the stomach by the dilute hydrochloric acid is 

 perhaps small in amount, but is of theoretic importance. 



When the acid reaches the duodenum it reacts on the prosecretin from 

 the gut- wall and produces secretin (see below). 



Aside from its hydrolytic powers this acid is a powerful antiseptic, 

 as are most other acids. The importance of this action we have no means 

 of estimating, but it must be considerable, for the bacteria which enter 

 the stomach with the food and drink are of numberless varieties and 

 of vast number. Some of these unchecked would derange all normal 

 digestion, while others would cause the illness or death of the individual. 

 The tubercle bacilli is not destroyed by gastric juice, but the germs 

 of anthrax and of cholera are quickly killed. Perhaps in the long run 

 the antiseptic action of the hydrochloric acid against the organisms of 

 ordinary putrefaction are more important to man than its destruction 

 of the virulent germs of disease. 



THE STOMACH'S FUNCTIONS. It will serve to fix the status of the 

 stomach in mind if its functions are arranged in a schematic list. Ten 

 sorts of usefulness may be noted, varying much in importance, but all 

 of benefit to the organism, the order in which they are given here being 

 apparently, in a general way, that of their relative importance. 



