CHAP. II.] THE COLOUR REACTIONS OF GASTRIC JUICE. 93 



Rabuteau's When starch mucilage is mixed with potassium 



reaction 1 . iodate and iodide, a solution is obtained which is blued 



by a dilute solution of hydrochloric acid, but not by a dilute solution 

 of lactic or acetic acid. The reagent employed by Rabuteau was made 

 by adding to 50 c.c. of starch mucilage 1 grm. of potassium iodate and 

 0'5 grm. of potassium iodide. Rabuteau found that the gastric juice 

 invariably caused a blueing of the solution, and this could not have 

 been the case had the gastric juice owed its acidity to an organic 

 acid. 



Reocn's J. Reoch 2 observed that a mixture of citrate of iron 



reaction. and quinine and of potassium sulphocyanide was coloured 



red by gastric juice, just as it is by a dilute solution of mineral acids, 

 whilst a dilute solution of organic acids does not lead to the formation 

 of the red colour. The reagent has been modified by Szab6 s and 

 employed in such a manner as to permit of an estimate of the amount 

 of mineral acid being found. 



Equal volumes of half per cent, solutions of ammonium sulpho- 

 cyanide and of potassio-sodic tartrate are mixed. One cubic centi- 

 metre of the pale yellow solution is coloured of a brownish-red colour 

 by the addition of 0*5 1*0 c.c. of a dilute hydrochloric acid containing 

 1 part of HC1 in 1000 parts, whilst a solution of lactic or of acetic 

 acids produce no reaction unless the acid amount to 15 or 20 

 per cent. 



With this reagent it can be shewn that the gastric juice of 

 healthy animals contains a mineral acid. 



Methyl- A solution of methyl-anilin violet is first of all ren- 



aniiin violet dered blue, then green, and ultimately decolourized by 

 dilute solutions of mineral acids, whilst dilute organic 

 acids do not affect the violet colour. The reaction was first observed 

 by Witz, then applied by Hilger to the detection of sulphuric acid in 

 vinegar. Maly 4 subsequently employed it in researches connected 

 with physiological chemistry. 



It would appear, however, from the observations of Ewald 5 and of 

 Uffelmann 6 that this reagent does not give perfectly reliable results 



1 Rabuteau, Gazette Medicale de Paris, 1874, p. 114. This author subsequently 

 confirmed the presence of HC1 in the gastric juice by a brilliant experiment. He found 

 that when quinine is added to the gastric juice, it is dissolved in considerable amount, 

 and he succeeded in separating in a perfectly pure and crystallized condition hydro- 

 chlorate and not lactate of quinine. Comptes Rendus, LXXX. (1875), p. 61. 



2 Reoch, ' The Acidity of the Gastric Juice. ' Journal of Anat. and Phys. , Vol. xiv. 

 (1874), p. 274. 



3 Szabd, 'Zur Kenntniss der freien Saure des menschlichen Magensaftes.' Zeit- 

 schriftf. phys. Chem., Vol. i. (1877), p. 153. 



4 Maly, ' Untersuchungen iiber die Mittel zur Saurebildung im Organismus,' &c. 

 Zeitschrift f. phys. Chemie, Vol. i. p. 174. (See ' Qualitativer Nachweis freier Salz- 

 sa'ure,' &c., p. 189.) 



5 C. A. Ewald, 'Ueber das angebliche Fehlen der freien Salzsaure im Magensafte.' 

 Zeitschr. /. klin. Medicin, i. 619. 



6 Uffelmann, ' Ueber die Methode der Untersuchung des Mageninhaltes auf freie 

 Sauren.' Archiv f. klin. Medicin, Vol. xxvi, p. 431. 



