194 PHYSIOLOGICAL CHEMISTRY. 



flakes are obtained and no solid coagulum. Addition of lime salts 

 is to be avoided, as they in great excess may produce a partial 

 coagulation even in the absence of rennet. 



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. Phenol phthalein must not be used as 

 an indicator, for we get too high results in the presence of large 

 quantities of albumin. Good results may be obtained, on the con- 

 trary, by using very delicate litmus-paper. As 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. Generally the acidity is 



~\t 

 expressed by the number of cc. of caustic soda which is required 



to neutralize the several acids in 100 cc. of the liquid of the stomach. 

 An acidity of 43$ means that 100 cc. of the liquid of the stomach 



required 43 cc. of caustic soda 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 pur- 

 pose, 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 quantities 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 con- 

 tents of the stomach. These reagents are a mixture of FERRIC 

 ACETATE and POTASSIUM SULPHOCYANIDE solution (MoHR's re- 

 agent is modified by several investigators), METHYL, ANILIN- 



VIOLET, TROP^OLIU 00, CONGO RED, MALACHITE-GREEN, PHLO- 



ROGLUCIN-YANILLIN, BENZOPURPURIN 6 B, 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 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 hydro- 

 chloric acid, MOHR'S test (even though not very delicate), GUNZ- 

 BURG'S test with phloroglucin-vanillin, and the test with tro- 

 paeolin 00, performed in moderate heat as suggested by BOAS, seem 

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

 presence of hydrochloric acid may be considered as proved. A 

 negative result does not eliminate the presence of hydrochloric acid, 

 as the delicacy of these reactions has a limit, and also the simul- 



