GASTRIC JUICE AND CHANGES IN STOMACH. 159 



detection of free acid, then, in such a case would be evidence 

 of relatively high secreting power. 



The Detection of Free Acid. In the early digestion stages 

 of a meal rich in carbohydrates organic acids, especially lactic 

 acid, may be formed by bacterial fermentation. But the 

 amount so produced is usually very small if the normal secre- 

 tion of hydrochloric acid begins in the proper time. The or- 

 ganic acids produced are in amounts ordinarily below o.i per 

 cent. Pathologically, when the bacterial fermentation goes on 

 unchecked by the production of hydrochloric acid, the organic 

 acid may accumulate far beyond this and may then be readily 

 detected by the processes given below. At present the detec- 

 tion of the free hydrochloric acid will be considered. Some 

 of the gastric secretion collected by a pump or otherwise is 

 filtered, and the filter (always a small one) is washed with a 

 very little water. The mixed filtrate and washings is used 

 for the following tests : 



DIMETHYLAMINOAZOBENZENE TEST. To a few cc. of the gastric filtrate 

 add a drop or two of this reagent used in weak alcoholic solution (about 

 0.2 per cent). Free hydrochloric acid present strikes a pink or even red 

 color with the indicator. Combined acid and the traces of organic acids 

 which may be present have no such action. 



CONGO RED TEST. This substance in aqueous solution is turned blue by 

 very dilute hydrochloric acid. Organic acids do not give the test, except 

 when present in relatively much stronger solution. 



The reaction is most conveniently carried out by means of test papers 

 made by dipping filter paper in a solution of the coloring matter and dry- 

 ing. These strips are dipped in the gastric filtrate and allowed to dry 

 spontaneously. 



METHYL- VIOLET TEST. A dilute violet-colored aqueous solution of this 

 substance, when mixed with weak hydrochloric acid, turns blue. The 

 reaction with gastric juice is faint, but when care is observed, characteris- 

 tic. Organic acids, even when present in quantity, do not give the test, 

 which was first successfully used for the detection of traces of mineral 

 acids in vinegar. Use a few drops with 2 cc. of the gastric filtrate. 



GUENZBERG'S REAGENT. This is a well-known solution and is made as 

 follows : 



Phloroglucin 2 grams 



Vanillin I gram 



Alcohol . . TOO cubic centimeters 



