GASTRIC DIGESTION. 1 29 



11. Tests for Lactic Acid, (a) Uffelmann's Reaction. To a 

 small quantity of Uffelmann's reagent 1 in a test-tube add a few 

 drops of a lactic acid solution. The amethyst-blue color of the 

 reagent is displaced by a straw yellow. Other organic acids give a 

 similar reaction. Mineral acids such as hydrochloric acid discharge 

 the blue coloration leaving a colorless solution. 



(&) Ferric Chloride Test. Place 10 c.c. of very dilute ferric 

 chloride in each of five tubes. To the first add 2 c.c. of 0.2 per 

 cent hydrochloric acid, to the second 2 c.c. of 10 per cent alcohol, 

 to the third 2 c.c. of 2 per cent sucrose, to the fourth 2 c.c. of 

 lactic acid and to the fifth 2 c.c. of peptone solution. 



It is evident from the results obtained that neither of the tests 

 given above is satisfactory for the detection of lactic acid in the 

 presence of other substances such as we find in the gastric contents. 



A satisfactory deduction regarding the presence of lactic acid can 

 only be made after extracting the gastric contents with ether, evapor- 

 ating the ether extract to dryness and dissolving the residue in water. 

 This residue will not contain any of the contaminations which in- 

 terfered with the simple tests as tried above, and therefore if either 

 of the tests is now tried on the dissolved residue of the ether extract 

 we may form an accurate conclusion regarding the presence of lactic 

 acid. 



(c) Hopkins' Thiophene Reaction. Place about 5 c.c. of concen- 

 trated sulphuric acid in a test-tube and add one drop of a saturated 

 solution of cupric sulphate. 2 Introduce a few drops of the solution 

 to be tested, shake the tube well and immerse it in the boiling 

 water of a beaker- water-bath for one or t\yo minutes. Now remove 

 the tube, cool it under running water, add 2-3 drops of a dilute 

 alcoholic solution 3 of thiophene, C 4 H 4 S, from a pipette, replace 

 the tube in the beaker and carefully observe any color change which 

 may occur. Lactic acid is indicated by the appearance of a bright 

 cherry-red color which forms rapidly. This color may be made 

 more or less permanent by cooling the tube as soon as the color is 

 produced. Excess of thiophene produces a deep yellow or brown 

 color with sulphuric acid. The test is not wholly specific though 

 the author claims it to be more so than Uffelmann's reaction. 



12. Qualitative Analysis of Stomach Contents. Take 100 c.c. 



1 Uffelmann's reagent is prepared by adding ferric chloride solution to a I per 

 cent solution of carbolic acid until an amethyst-blue color is obtained. 



2 This is added to catalyze the oxidation which follows. 



3 About 10-20 drops in 100 c.c. of 95 per cent alcohol. 



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