88 THE GASTRIC JUICE. 



meters more of the filtered gastric juice and add about a gramme 

 of finely-powdered calcium carbonate. Stir well and filter through 

 a dry paper. Measure 10 cubic centimeters of the filtrate into a 

 small flask and by means of a rubber bulb or aspirator (not with 

 the lungs) blow air through it to remove the carbon dioxid. Then 

 add 5 cubic centimeters of the calcium chlorid solution and phenol- 

 phthalein and neutralize with standard sodium hydrate as before. 

 Since the free acids are neutralized by the calcium carbonate, the 

 sodium hydrate used in this second determination corresponds to 

 the acid phosphates, and the difference between the two to the 

 free acid. 



Subtract the number of cubic centimeters of alkali used in the 

 last determination from that used in the first. If lactic and volatile 

 acids are present and have been determined, subtract also the 

 number of cubic centimeters required to neutralize them. The 

 remainder has been used to neutralize the hydrochloric acid. Cal- 

 culate the percentage of the latter, remembering that 1 cubic centi- 

 meter of sodium hydrate equals 0.00364 gramme of hydrochloric 

 acid. 



Lactic acid changes a mixture of gentian violet and 

 ferric chlorid to a green or greenish yellow. None of the 

 other normal or pathological constituents of the gastric 

 juice appear to do the same or to interfere with the use of 

 the above reagents in testing for the lactic acid. 



Lactic acid can also be detected in the gastric juice by 

 the yellow color which it imparts to a solution of ferric 

 chlorid or to the amethyst solution which is produced by 

 adding ferric chlorid to carbolic acid (phenol), although 

 glucose or alcohol gives a similar color. 



It is generally unnecessary to determine the quantity of 

 lactic acid. If this is desired it can be done by measuring off 10 

 cubic centimeters of the juice, diluting to about 100 cubic centi- 

 meters and distilling off the acetic and butyric acids, which can 

 be determined in the distillate. After the volatile acids have been 

 removed by distillation until the liquid remaining is about 10 or 

 20 cubic centimeters, the lactic acid can be dissolved from the 

 residue by shaking it six times with 100 cubic centimeters of 



