35 FOOD AND DIGESTION 



logical conditions it may be entirely absent, or may amount to 0.5 per cent., 

 or even more. 



Hydrochloric acid is the proper acid of healthy gastric juice, and various 

 tests have been used to prove this. The tests depend upon changes produced 

 in aniline colors by the action of hydrochloric acid even in minute traces, 

 whereas lactic and other organic acids have no such action. 



An aqueous solution of oo-tropeolin, a bright yellow dye, is turned red on 

 the addition of a minute trace of hydrochloric acid, and aqueous solutions 

 of methyl violet and gentian violet are turned blue under the same circum- 

 stances. The lactic acid sometimes present in the contents of the stomach is 

 derived partly from the sarcolactic acid of muscle and partly from lactic-acid 

 fermentation of carbohydrates. Lactic acid (C 3 H 6 O 3 ), if present, gives the 

 following test: A solution of 10 cubic centimeters of a 4 per cent, aqueous 

 solution of carbolic acid, 20 cubic centimeters of water, and one drop of ferric 

 chloride is made; forming a blue-colored mixture. A mere trace of free lactic 

 acid added to such a solution causes it to become yellow. Inasmuch as 

 mineral acids also discharge the color, the lactic acid is removed from the 

 gastric contents by shaking with ether and trying the test with the solution 

 of the residue after evaporation of the ether. 



The protein matter in the food combines to some extent with the hydro- 

 chloric acid, which then is known as combined acid and does not redden litmus- 

 paper. As this combination is immediate, it follows that no free acid is found 

 in the gastric contents until the amount secreted is more than enough to satu- 

 rate the various albuminous affinities. It is partly for this reason that, as al- 

 ready mentioned, salivary digestion may continue in the stomach for some 

 time after the commencement of gastric digestion. According to Ehrlich, the 

 amount necessary to saturate the affinities of 100 grams of various articles 

 of diet is as follows: 



Beef (boiled) 2.0 grams of pure HC1. 



Mutton (boiled) 1.9 grams of pure HC1. 



Veal (boiled) 2.2 grams of pure HC1. 



Pork (boiled) 1.6 grams of pure HC1. 



Ham (boiled) 1.8 grams of pure HC1. 



Sweetbread (boiled) 0.9 gram of pure HC1. 



Wheat bread 0.3 gram of pure HC1. 



Rye bread 0.5 gram of pure HC1. 



Swiss cheese 2.6 grams of pure HC1. 



Milk (100 c.c.) o . 32-0 .42 gram of pure HC1. 



The acid is chiefly found at the surface of the mucous membrane, but is 

 in all probability formed by the parietal cells of the cardiac glands, hence 

 called oxyntic, for no acid is formed by the pyloric glands in which this 

 variety of cell is absent. It seems established that the chlorides of the blood 

 are the source of the hydrochloric acid, for when these chloride salts are 



