230 PRACTICAL PHYSIOLOGY 



below), it may be found even higher than that of normal 

 gastric contents. By the application of the indicator tests (especially 

 Giinzberg's), it can readily be shown that the acidity is not due 

 to free hydrochloric acid. This leaves, as its possible causes, 

 hydrochloric acid combined with protein, acid salts, and organic 

 acids. Since it is known that bacteria may produce organic acids, 

 especially lactic acid, this acid should be looked for. 



A simple presumptive test for the presence of lactic acid especially 

 in the absence of hydrochloric acid is that of Uffelmann. Add to 

 about 5 c.c. of Uffelmann's reagent (50 c.c. of 4 per cent, carbolic 

 acid to which a drop of liq. ferri perchloridi is added) a drop or 

 two of the solution suspected to contain lactic acid. If it be pre- 

 sent the violet coloured Uffelmann reagent turns canary yellow. 

 Hydrochloric acid discharges the violet colour. If both lactic and 

 hydrochloric acids be present, they must be separated by shaking 

 the solution, or gastric contents (5 c.c. with 30 c.c. ether) with ether 

 in a separating funnel. Lactic acid is soluble in ether whereas 

 hydrochloric acid is not. If the yellow colour is still given by the 

 ethereal solution, it may be presumed that lactic acid is present. 

 This can be confirmed by the thiophene test. 



A much more sensitive and characteristic test for lactic acid is the thio- 

 phene test of Hopkins', which is applied as follows : 



EXPERIMENT IV. Mix some of the water-free ethereal extract of stomach 

 contents with 5 c.c. concentrated sulphuric acid, and transfer to a dry test 

 tube. Add 3 drops of a saturated solution of copper sulphate, mix, heat the 

 mixture in a boiling water bath for two minutes. Cool under the tap, and 

 add 2 drops of a 0-2 per cent, alcoholic solution of thiophene and shake. 

 Replace the tube in the boiling water bath. A cherry red colour will 

 develop if lactic acid is present. Examine the solution frequently during 

 the heating as prolonged heating causes the solution to become very dark. 



The lactic acid is produced by the action of the bacillus acidi lactici and other 

 organisms on sugars (see Milk, p. 328). 



C 12 H 22 U + H 2 = 4C 3 H 6 3 

 Lactose. Lactic acid. 



The fermentative process seldom stops at the production of lactic acid. 

 Other bacteria act on the lactic acid and produce butyric acid, carbon dioxide 

 gas, and hydrogen. 



4C 3 H 6 3 = 2C 4 H 8 2 + 4C0 2 + 4H 2 

 Lactic acid. Butyric acid. 



These gases accumulate in the stomach, causing flatulence. The presence 

 of butyric acid usually reveals itself by the odour of the gastric contents. 

 When its presence is doubtful, boil a portion of the fluid and hold a strip of 

 blue litmus paper in the steam. If this turns red, it indicates a volatile acid 

 (butyric or acetic). Butyric acid has a characteristic odour. 



Acid phosphates (NaH 2 Po 4 ) when present in gastric contents are demon- 

 strated by mixing calcium carbonate with a portion of the fluid. If an acid 

 reaction still remains towards litmus paper, acid phosphates must be present, 

 since the calcium carbonate will have combined with the free acids. 



In the clinical examination of the stomach contents numerous methods have 

 been introduced for the purpose of estimating the total acidity, the total amount 

 of hydrochloric acid, and the amount of free (uncombined) hydrochloric acid 

 contained therein. A brief outline of one of the most useful is given below. 



1. Total Acidity. A measured quantity (10 c.c.) of filtered gastric contents 

 is mixed in an Erlenmeyer flask with ten times its bulk of di stilled water. Two 



