ANIMAL FLUIDS AND TISSUES. 437 



Phloroglucin-vanittin. This reagent is made by dissolving 2 parts 

 of phloroglucin and 1 part of vanillin in 30 parts of alcohol. It is 

 a very sensitive and reliable reagent for the detection of free hydro- 

 chloric acid. Five drops of the solution mixed with an equal quan- 

 tity of gastric filtrate are gently heated over a Bunsen flame. On 

 complete evaporation a distinct red color or tinge appears in the 

 presence of not less than 0.01 per cent, of hydrochloric acid. The 

 formation of cherry-red crystals indicates the presence of large 

 quantities of the acid. Organic acids have no action on this reagent. 



Resorcin. This reagent is equally as sensitive as, and more stable 

 than, phloroglucin-vanillin. The solution is obtained by dissolving 

 5 parts of resublimed resorcin and 3 parts of cane-sugar in 100 parts 

 of dilute alcohol. The manner of testing with this reagent is the 

 same as described above for phloroglucin-vanillin ; a bright-red tinge 

 or color appears, even when very small quantities of free hydrochloric 

 acid are present. 



d. Lactic acid. Uffelmann's reagent answers best for detecting 

 this acid. It is made by adding 1 or 2 drops of ferric chloride 

 solution to 10 c.c. of a 1 per cent, carbolic acid solution, and diluting 

 this solution with water until it assumes an amethyst-blue color. 

 To 2 c.c. of this solution an equal volume of gastric-juice is added. 

 In the presence of at least 0.01 per cent, of lactic acid the liquid 

 assumes a pure yellow color. As the presence of too much hydro- 

 chloric acid (or even of some other substances) prevents the change, 

 it is well to shake (in doubtful cases) 10 c.c. of juice with 50 c.c. of 

 ether, evaporating the ethereal solution to dryness, dissolving the 

 residue in a few drops of water, and adding to this solution, which 

 contains the lactic acid, the above reagent. 



Butyric acid changes Uffelmann's reagent to brownish-yellow. 

 Butyric and acetic acid may both be recognized by their odor. 



e Total acidity. This is best determined by titration with an 

 alkali ; the estimation is conducted as follows : To 10 c.c. of the 

 filtered liquid a few drops of phenol-phtalein solution are added, and 

 to the mixture deci-normal potassium hydroxide solution is slowly 

 added from a burette until the liquid assumes- a slight reddish tint, 

 which does not disappear on stirring. 



It is customary to express the acidity in percentages, according to 

 the quantity of deci-normal potassium hydroxide used. Thus, 52 

 per cent, acidity would indicate that every 100 c.c. of gastric filtrate 

 are exactly neutralized by 52 c.c. of deci-normal potassium hydroxide. 



Though the total acidity is due to a mixture of hydrochloric acid, 



