36 PHYSIOLOGICAL AND PATHOLOGICAL CHEMISTRY. 



1. Add a few drops of the reagent to some of the stronger 

 hydrochloric acid solution A: decolorization. 



2. Repeat with the lactic acid solution: lemon-yellow 

 color. 



3. Repeat with a mixture of equal parts of the hydro- 

 chloric acid solution A and lactic acid: lemon-yellow color, 

 but fainter than in 2. Conclusion: lactic acid in the pres- 

 ence of hydrochloric acid may be detected by Uffelmann's 

 reagent, but not hydrochloric acid in the presence of lactic 

 acid. 



4. Add to 15 cc. of the lactic acid solution some of Uffel- 

 mann's reagent and divide into three parts, A, B, and C. 

 To A add its own volume of water, to B the same volume of 

 a concentrated salt solution, to C the same volume of a 3 per 

 cent, salt solution: only B is decolorized; the presence of 

 sodium chloride, therefore does not as a rule interfere with 

 the detection of lactic acid. 



(6) After Isolating the Lactic Acid by Means of Ether. Mix 

 25 cc. of the hydrochloric acid solution A with 25 cc. of the 

 lactic acid solution, shake with 50 cc. of ether, separate the 

 ether and shake the aqueous fluid again with ether. Filter 

 the united ether extracts through a dry filter and distil off 

 the ether. Take up the residue in a little water and test the 

 solution with Uffelmann's reagent. This method of isolat- 

 ing the lactic acid by means of ether is used especially with 

 the fluids of the stomach when their color prevents or ren- 

 ders difficult the direct detection of the lactic acid. 



III. DETECTION OF PEPSIN IN THE GASTRIC JUICE OR 



VOMIT. 



Add to 10 or 20 cc. of the fluid 10 to 20 drops of pure 

 dilute hydrochloric acid (1 : 10), then add some shreds of 

 fibrin or a slice of hard-boiled egg-albumen, and keep the 

 mixture at 40. The shreds of fibrin should dissolve even to 



