122 THE D1GKST1V1-: FLUIDS. 



described, by separately estimating tin- amount of free hydrochloric 

 acid by Topfer's method, and deducting the result from the total 

 amount of the physiologically active acid. More accurate results 

 are probably reached in this manner than with Topi'er's method, 

 unless some experience has been gained in the titration with alizarin. 



Should organic acids also be present, their amount may be esti- 

 mated by deducting from the total acidity the result reached with 

 the above method. 



If monophosphates are present at the same time, the resulting 

 figures will be a little too low; but the error which is thus incurred 

 is trifling. It may be obviated, however, by making use of L< <> ~ 

 method (see above). 



Lactic Acid. Tests for Lactic Acid. In order to assure our- 

 selves that any lactic acid that may be found in the gastric contents 

 has not been introduced into the stomach from without, it is neces- 

 sary to make such examinations after the administration of a test- 

 meal, in which the acid in question does not occur preformed. The 

 meal which is almost exclusively used for this purpose in clinical 

 work is the so-called test-meal of Boas. It consists of a plateful 

 of oatmeal soup, which is prepared by adding a tablespoonful of 

 rolled oats and a little salt to a liter of water, and boiling down to 

 about 500 c.c. The contents of the stomach are then drawn off 

 after one hour, filtered, and treated as described below. 



UFFELMANN'S TEST. About 10 c.c. of the filtered gastric con- 

 tents are extracted with ether (50-100 c.c.) by shaking in a sepa- 

 rating funnel for from tw r enty to thirty minutes. The ethereal ex- 

 tract is then evaporated to dryness by distilling on a water-bath ; 

 the residue is taken up with a few cubic centimeters of distilled 

 water, and treated as follows : 3 drops of a saturated aqueous solu- 

 tion of ferric chloride are mixed with an equal number of drops of a 

 concentrated solution of pure carbolic acid, and diluted with water 

 until a light-amethyst color is obtained. To this solution a portion 

 of the ethereal extract is added, when in the presence of lactic acid a 

 lemon or canary color develops. 



The delicacy of the test is such that the presence of 0.1 per cent, 

 of lactic acid can be demonstrated. 



KELLING'S TEST. Five or 10 c.c. of the filtered stomach-contents 

 are diluted from ten to twenty times with water and treated with 1 

 or 2 drops of a 5 per cent, aqueous solution of ferric chloride. In 

 the presence of lactic acid a distinct greenish-yellow 7 color is obtained 

 when the tube is held to the light. 



BOAS' TEST. This test is more accurate than the two just de- 

 scribed, but more time-consuming and complicated. It is based 

 upon the decomposition of lactic acid into formic acid and acetic 

 aldehyde, and the demonstration of the presence of the latter. To 

 this end, from 10 to 20 c.c. of the filtered stomach-contents are 

 treated with a slight excess of barium carbonate, and evaporated on 

 a water-bath. The resulting syrup is acidified with a few drops 



