GASTKIC DIGESTION. 351 



dignity of a demonstration. It is known that the acid is formed only 

 by the parietal cells of the gastric tubules, and the free acid is found on 

 the free surface of the gastric mucous membrane. An experiment 

 devised by Bernard serves to demonstrate this. For the production of 

 Prussian blue through the union of potassium ferroc3'anide and a salt 

 of iron, an acid reaction is requisite. Claude Bernard injected potassium 

 ferrocyanide, and afterward a solution of lactate of iron into the veins 

 of a dog. When examined after death, the blue color was found only in 

 the upper layers of the gastric mucous membrane, showing thus that 

 this locality was the sole seat of the acid reaction. As to the origin of 

 this acidity, it appears that the parietal cells of the gastric glands form 

 hydrochloric acid from the chlorides which the mucous membrane takes 

 up from the blood; for, if sodium chloride be withheld from the food, 

 the formation of hydrochloric acid ceases. The active agent in this 

 splitting up of the chlorides is probably lactic acid, which, by splitting 

 up sodium chloride, forms free hydrochloric acid, while the bases, forming 

 alkaline salts, are excreted by the urine. The renal secretion is, there- 

 fore, less acid during digestion than in the intervals of digestion. 



The following tables represent the quantitative composition of gastric 

 juice in different animals : 



Water 



Organic matter (especially ferments), 

 Sodium chloride, .... 

 Calcium chloride, . 

 Hydrochloric acid, . . 

 Potassium chloride, ., -. .. 

 Ammonium chloride, ..,.. 

 Calcium phosphate, ) 



Magnesium " > , 0.125 



Ferric " ) 



2. THE ACTION OF GASTRIC JUICE ON THE FOOD. The general solvent 

 effects of the gastric juice on food-stuffs may be roughty illustrated by 

 means of an experiment devised by Schiff, in which the stomach, removed 

 from the body and placed in an acid medium, is capable of digesting 

 itself. If the stomach is removed from a dog, minced into small pieces, 

 and infused in four or five hundred cubic centimeters of HC1 of 0.02 

 per cent, in an oven at 40 C., at the end of eight to ten hours the 

 fragments of the stomach will be found to be almost entirely liquefied. 

 In the structures of the stomach are found the principal animal sub- 

 stances which serve as nutriment. Albumen and fibrin of the blood are 

 present, muscular tissue, and connective tissue. These substances then 

 being dissolved, as may be demonstrated by the fact that the liquid, 

 which may be filtered off from the small, pulpy and yellowish residue, is 

 free from solid material, it remains only to determine in what form these 

 albuminoid constituents of the tissues are present in the solution. 



