THE GASTRIC JUICE. 131 



dimethyl-amino-azobenzol, when in the presence of free hydro- 

 chloric acid a beautiful cherry-red color develops at once, which 

 varies in intensity with the amount of the free acid present. Com- 

 bined hydrochloric acid, as well as acid salts and organic acids, in 

 the concentration in which they may be met with in the stomach- 

 contents, do not produce this color. 



The delicacy of the reagent is such that the normal yellow color 

 of the indicator is changed to a reddish tinge upon the addition of 

 but one drop of a -fa normal solution of hydrochloric acid in 5 c.c. 

 of distilled water, viz., 0.7 per cent. 



GUNZBURG'S TEST. The reagent consists of 2 grammes of phloro- 

 glucin and 1 gramme of vanillin, dissolved in 100 grammes of 

 80 per cent, alcohol. It should be kept in a dark-colored, glass- 

 stoppered bottle. 



A few drops of the filtered gastric contents are carefully evapo- 

 rated with an equal amount of the reagent on a plate of thin porce- 

 lain or glass, when in the presence of free hydrochloric acid a 

 rose-colored mirror is obtained, which varies in intensity with the 

 amount of the acid. 



Organic acids do not produce the reaction. 



The delicacy of the test is such that the presence of 0.05 gramme 

 of hydrochloric acid in 100 parts of water can be demonstrated. 



BOAS' TEST. The reagent consists of 5 grammes of resublimed 

 resorcin and 3 grammes of cane-sugar, dissolved in 100 grammes 

 of 94 per cent, alcohol. The test is conducted like that of Giinz- 

 burg, but it is necessary to heat a little more strongly, especially 

 after the fluid has been evaporated. A similarly colored mirror is 

 obtained, which gradually fades on cooling. 



The delicacy of the test is the same as that of Giinzburg. 



Examination for the Presence of Combined Hydrochloric Acid. 

 The presence of combined hydrochloric acid cannot be demonstrated 

 by means of simple tests like those, just described, but is inferred 

 indirectly, as shown in the following method : 



Separate Estimation of the Free and Combined Hydrochloric Acid 

 of the Gastric Contents. TOPPER'S METHOD. The total acidity of 

 a given amount of the gastric contents is first determined, as 

 already described, and termed A. This indicates the amount of 

 the physiologically active hydrochloric acid, viz., the free and the 

 combined hydrochloric acid, as well as that of any acid salts and 

 organic acids that may be present. 



In a second specimen the total amount of free acids and acid 

 salts is determined by titrating, as before, with a -fa normal solu- 

 tion of sodium hydrate, but using a few drops of a saturated 

 aqueous solution of alizarin (alizarin-monosulphonate of sodium) as 

 an indicator. The titration is carried to a point where a pure violet 

 color is obtained. The result is termed B. The difference between 

 A and B is thus referable to the presence of the combined hydro- 

 chloric acid, and termed C. 



