464 DIGESTION. 



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

 mercury with NESSLER'S reagent. CRONER and CRONHEIM l 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 hydrochloric 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 that 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. ScntTTz. 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 defined whether one wishes 

 to determine the actually free or the physiologically active hydro- 

 chloric acid before any conclusions are drawn as to the value of a certain 

 reaction. 



The acid reaction may be partly due to free acid, partly to acid salts (mono- 

 phosphates), and partly to both. According to LEO 4 one can test for acid phos- 

 phates by calcium carbonate, which is not neutralized therewith, while the free 

 acids are. If the gastric content has a neutral reaction after shaking with cal- 

 'cium carbonate and the carbon dioxide is driven out by a current of air, it 

 contains only free acid; if it has an acid reaction, acid phosphates are present, 

 :and if it is less acid than before, it contains both free acid and acid phosphate. 

 It must not be forgotten that a faint acid reaction may, after treatment with cal- 

 cium carbonate, also be due to the protein. This method can likewise be applied 

 in the estimation of free acid. 



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

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

 physiol. Chem., 50. 



2 Bioch. Zeitschr., 12. 



3 Alb. Miiller, Deutsch. Arch. f. klin. Med., 88, and Pflitger's Arch., 116; J. Schiitz,. 

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



4 Centralbl. f. d. med. Wissensch., 1889, p. 481; Pfliiger's Arch., 48, and Berlin, 

 klin. Wochenschr., 1905, p. 1491. 



