12 GASTRIC DIGESTION OF PROTEINS 



large "partridge-shell" snail, Dolium galea, on coming in 

 contact with the marble tiles with which the room was paved, 

 caused an effervescence just as if some strong acid had been 

 dropped upon the tile. Since then we have come to know 

 that a number of marine snails secrete an acid salivary fluid, 

 and that that of Dolium contains appreciable amounts of 

 free sulphuric acid. 26 



Determination of Acidity of Gastric Juice. In any 

 observation relative to acid secretion in the gastric juice 

 the quantitative determination of the free hydrochloric 

 acid is naturally a matter of much importance; some of 

 the more definite advancements of method deserving brief 

 mention at this time. A number of new features have been 

 added to the old color reactions for the recognition of free 

 hydrochloric acid, as the employment in modification of 

 Giinzberg's reagent of a mixture of p-oxybenzaldehyde with 

 phloroglucin or of a mixture of dimethylamidobenzaldehyde 

 with indol. It is of more importance, however, that we 

 have come to recognize that estimation of the true acidity 

 of the gastric juice, that is, its hydrogen ion concentration, is 

 impossible by simple titration. For this we need either 

 measurement of the electromotor power of the actual 

 hydrogen-concentration chains 27 or the indicator method. 

 In Miiller's method gastric juice is mixed with a solution of 

 tropaeolin; the fluid then assumes a color, which ranges ac- 

 cording to the degree of acidity between a reddish brown and 

 yellow, and by comparison with a color scale the percentage 

 presence of "free hydrochloric acid" can be directly de- 

 termined. 28 The method of Dreser 29 is based on quite a 



36 Literature upon Acid Secretion in Gastropoda: O. v. Fiirth, Ver- 

 gleichende chemische Physiologie der niederen Tiere, pp. 208-215, Jena, 1903. 



27 C. Foa, C. R. Soc. de Biol., 1905, I, 865; II, 2; F. Tangl, Pfliiger's Arch., 

 115, 64, 1906. L. Michaelis and H. Davidsohn, Zeitschr. f. exper. Pathol. 8, 

 398, 1910; J. Christiansen (Copenhagen), Deutsche Arch. f. klin. Med., 102, 

 103, 1911. 



88 A. Mtiller (Clinic of v. Noorden, Vienna), Med. Klinik, 1909, 1438. 



"H. Dreser, Hofmeister's Beitr., 8, 285, 1906. 



