INVESTIGATION OF THE GASTRIC CONTENTS. 453 



should coagulate at room temperature within 10-20 minutes without 

 changing its reaction. The addition of lime salts is unnecessary, and 

 may readily lead to erroneous conclusions. 



In many cases it is especially important to determine the degree of 

 acidity of the gastric juice. This may be done by the ordinary titration 

 methods. Phenolphthalein must not be used as an indicator, as too 

 high results are produced in the presence of large quantities of proteins. 

 Good results may be obtained, on the contrary, by using very delicate 

 litmus paper. Although the acid reaction of the contents of the stomach 

 may be caused simultaneously by several acids, still the degree of acidity 

 is here, as in other cases, expressed in only one acid, e.g., HC1. Gen- 

 erally the acidity is designated by the number of cubic centimeters of 

 N/10 sodium hydroxide required to neutralize the several acids in 

 100 cc. of the liquid of the stomach. An acidity of 43 per cent means 

 that 100 cc. of the liquid of the stomach required 43 cc. of N/10 sodium 

 hydroxide to neutralize it. 



It is also important to be able to ascertain the nature of the acid or 

 acids occurring in the contents of the stomach. For this purpose, and 

 especially for the detection of free hydrochloric acid, a great number of color 

 reactions have been proposed which are all based upon the fact that the 

 coloring substance gives a characteristic color with very small quanti- 

 ties of hydrochloric acid, while lactic acid and the other organic acids 

 do not give these colorations, or only in a certain concentration, which 

 can hardly exist in the contents of the stomach. These reagents are a 

 mixture of FERRIC-ACETATE and POTASSIUM-SULPHOCYANIDE solutions 

 (MOHR'S reagent has been modified by several investigators), METHYL- 

 ANILINE-VIOLET, TROP^OLIN 00, CONGO RED, MALACHITE-GREEN, PHLORO- 



GLUCINOL-VANILLIN, DiMETHYLAMiNOAZOBENZENE, and others. As reagents 

 for free Lactic acid UFFELMANN suggests a strongly diluted, amethyst- 

 blue solution of FERRIC CHLORIDE and CARBOLIC ACID or a strongly diluted, 

 nearly colorless solution of FERRIC CHLORIDE. These give a yellow 

 color with lactic acid, but not with hydrochloric acid or with volatile 

 fatty acids. 



The value of these reagents in testing for free hydrochloric acid or lactic 

 acid is still disputed. Among the reagents for free hydrochloric acid it seems 

 STEENSMA s l modification of GUNZBURG'S test with phloroglucinol-vanillin, and 

 the test with tropseolin 00, performed at a moderate temperature as suggested by 

 BOAS, and the test with dimethylaminoazobenzene, which is the most delicate, 

 seem to be the most valuable. If these tests give positive results, then the presence 

 of hydrochloric acid may be considered as proven. A negative result does not 

 eliminate the presence of hydrochloric acid, as the delicacy of these reactions 

 has a limit, and also the simultaneous presence of protein, peptones, and other 

 bodies influences the reactions more or less. The reactions for lactic acid may 

 also give negative results in the presence of comparatively large quantities of 

 hydrochloric acid in the liquid to be tested. Sugar, sulphocyanides, and other 

 bodies may act with these reagents like lactic acid. 



In testing for lactic acid it is safest to shake the material with ether and test 

 the residue after the evaporation of the solvent. On the evaporation of the ether 

 the residue may be tested in several ways. BOAS utilizes the property possessed 

 by lactic acid of being oxidized into aldehyde and formic acid on careful oxida- 

 tion with sulphuric acid and manganese dioxide. The aldehyde is detected by 



1 Bioch. Zeitschrift, 8. 



