488 DIGESTION. 



the test with tropseolin 00, performed at a moderate temperature as suggested by 

 BOAS, and the test with dimethylaminoazobenzene, which is the most delicate, 

 seem to be the most valuable. If these tests give positive results, then the presence 

 of hydrochloric acid may be considered as proved. A negative result does not 

 eliminate the presence of hydrochloric acid, as the delicacy of these reactions 

 has a limit, and also the simultaneous presence of protein, peptones, and other 

 bodies influences the reactions more or less. The reactions for lactic acid may 

 also give negative results in the presence of comparatively large quantities of 

 hydrochloric acid in the liquid to be tested. Sugar, sulphocyanides, and other 

 bodies may act with these reagents like lactic acid. 



In testing for lactic acid it is safest to shake the material with ether and test 

 the residue after the evaporation of the solvent. On the evaporation of the ether 

 the residue may be tested in several ways. BOAS utilizes the property possessed 

 by lactic acid of being converted into aldehyde and formic acid on careful oxida- 

 tion with sulphuric acid and manganese dioxide. The aldehyde is detected by 

 its forming iodoform with an alkaline iodine solution or by its forming aldehyde- 

 mercury with NESSLER'S reagent. CRONER and CRONHEIM * have suggested 

 another method. 



The quantitative estimation consists in the formation of iodoform with N/10 

 iodine solution and caustic potash, adding an excess of hydrochloric acid and 

 titrating with a N/10 sodium-arsenite solution, and retitrating with iodine solu- 

 tion, after the addition of starch-paste, until a blue coloration is obtained. This 

 method presupposes the use of ether entirely free from alcohol. For details see 

 the original publication and the modification of this method suggested by 



JERUSALEM. 2 



In order to be able to judge correctly of the value of the different 

 reagents for free hydrochloric acid, it is naturally of greatest importance 

 to be clear in regard to what we mean by free hydrochloric acid. It is 

 a well-known fact that hydrochloric acid combines with proteins, and a 

 considerable part of the hydrocholoric acid may therefore exist in the 

 contents of the stomach, after a meal rich in proteins, in combination 

 with them. This hydrochloric acid combined with proteins cannot 

 be considered as free, and it is for this reason that certain investigators 

 consider such methods as those of SJOQVIST, which will be described 

 below, as of little value. However, it must be remarked that, according 

 to the unanimous experience of many investigators, the hydrochloric 

 acid combined with proteins is physiologically active and in this regard 

 we must refer to the recent investigations of ALB. MULLER and J. ScnuTz. 3 

 Those reactions (color reactions) which only respond to actually free 

 hydrochloric acid do not show the physiologically active hydrochloric 

 acid. The suggestion of determining the " physiologically active " 

 hydrochloric acid instead of the " free " seems to be correct in principle; 

 and as the conceptions of free and of physiologically active hydrochloric 

 acid are not the same, it must always be well denned whether one wishes 

 to determine the actually free or the physiologically active hydro- 



1 Boas. Deutsch. med. Wochenschr., 1893, and Miinchener med. Wochenschr. 1893, 

 Croner and Cronheim, Berl. klin. Wochenschr., 1905. See also Thomas, Zeitschr. f. 

 physiol. Chem., 50. 



2 Bioch. Zeitschr., 12. 



8 Alb. M'iiller, Deutsch. Arch. f. klin. Med., 88, and Pfliiger's Arch., 116; J. Schiitz. 

 Wien, klin. Wochenschr., 20, and Wien. med. Wochenschr., 1906 (older literature). 



