FORMATION OF HYDROCHLORIC ACID IN THE FOVEOUE. 24! 



It is also clear that in order to solve this problem by the use 

 of a chemical indicator the substance employed, in addition to 

 being an indicator of acidity or alkalinity, must have the prop- 

 erties of a vital stain, that is to say, the cells of the gastric glands 

 must be freely permeable to it and it must have a special affinity 

 for constituents of the gastric secretion in the glands, or the 

 distribution coefficient must favor its concentration in this 

 secretion in sufficient amounts to give a distinct color reaction. 

 These conditions we have found to be fulfilled by neutral red 

 and by a number of dyes belonging to the naphtol blue series 

 including nile blue, and the various cyanamins discovered by 

 Witt ('90). 



Our first successful experiments in staining specifically the 

 secretion in the parietal cells and in the lumina of the gastric 

 glands were obtained with Griibler's napthalin blue R crystals 

 (a trade name for naphtol blue). Solutions of this dye in normal 

 salt solution, injected into the blood vessels of the recently killed 

 animal, were found to stain the secretion in the canaliculi of the 

 parietal cells and in the lumina of the gland tubules of the fundus 

 region a distinct red color, while the cells of the foveola and the 

 mucus on the free surface were stained a deep blue. 



Tests of the solution of naphtalin blue afforded no explana- 

 tion of this result, inasmuch as addition of acid produced no 

 change in the color of the solution, and addition of sodium 

 hydrate gave a green color. Accordingly, it seemed probable 

 that the reaction observed was due either to another dye present 

 in the naphtalin blue as an impurity, or to a new dye synthesized 

 during the process of staining. 



After consideration of the commercial process for the manu- 

 facture of the naphtol blues it seemed probable, in view of the 

 fact that dimethylparaphenylendiamin is a biproduct of the 

 synthesis of naphtol blue from nitrosodimethylanilin and B 

 naphtol, that the dye on which this reaction depended would 

 prove to be cyanamin, which, according to Witt, is formed when 

 the mixture of naphtol blue and dimethylparaphenylendiamin 

 resulting from the synthesis above mentioned is boiled for a time 

 with an alcoholic solution of potassium hydroxide. Accordingly, 

 cyanamin chloride was prepared by the process described by 

 Witt, and its solutions tested on the gastric mucous membrane. 



