156 PHYSIOLOGICAL CHEMISTRY 



ject of much study. The total acidity of the gastric contents is 

 due to the sum of several factors, free hydrochloric acid, hydro- 

 chloric acid combined with protein, acid salts and small amounts 

 of organic acids. It may be determined as follows. The pa- 

 tient, in the morning, when the stomach is empty, is required 

 to eat a ' ' test meal, ' ' which consists of a cup of tea and a piece 

 of toast, or some other simple articles of diet. At the end of a 

 specified time, for example forty-five minutes or one hour, the 

 patient is made to vomit, or his stomach is pumped out with a 

 stomach pump. A measured amount of the unfiltered stomach 

 contents is titrated with N/10 NaOH using phenolphthalein as 

 indicator. This indicator is sensitive to such small amounts of 

 hydrogen-ions (thus to such weak acidity) that the method will 

 yield results corresponding to the total acidity from all factors. 

 100 c.c. of normal gastric contents should require about 74 c.c. 

 to 90 c.c. of N/10 NaOH to neutralize it. By the use of other 

 indicators which are less sensitive to weak acids, it is possible 

 to decide whether all of the acidity is due to free hydrochloric 

 acid, or part of it to hydrochloric acid combined with protein or 

 to weaker acids. Gunzberg's and Toepfer's reagents are the best 

 indicators to determine free hydrochloric acid. It is obvious 

 that a large amount of a weak acid will produce as high a con- 

 centration of hydrogen-ions as a small amount of a strong acid. 

 For this reason the above methods, and other similar methods 

 for determining the various factors making up total acidity 

 are inaccurate. The accurate determination of hydrogen-ion 

 concentration is made by the gas chain method, a process which 

 is too difficult for the average physician. The following method 

 gives approximately correct results. It consists in using Gunz- 

 berg's reagent, which contains 2 g. phlorglucin, and 1 g. vanil- 

 lin to 100 c.c. alcohol. The reagent should be kept in the dark. 

 A drop of the reagent on a white plate is dried on the water 

 bath. A drop of the juice to be tested is added to the yellow 

 spot. On warming, if free hydrochloric acid is present a red 

 color develops. By diluting, a point will be found where the 

 liquid just gives the reaction. At this point the concentration 



