Just here we may recall the theory advanced by Richet[107] quite a number of years ago that the acid of the gastric juice is a conjugate acid, composed of leucin and hydrochloric acid, a theory which has found little acceptance. Klemperer,[108] however, assumed that solutions of leucin hydrochloride with pepsin would not digest albumin, but Salkowski and Kumagawa[109] have shown by experiments that leucin and other amido-acids, as glycocoll, may be dissolved in hydrochloric acid in such proportion that the solution is practically composed of leucin hydrochloride, without interfering with the digestive action of pepsin-acid on blood-fibrin; the solution being physiologically active, although Günzburg’s reagent shows an entirely negative result for free acid. If the matter is studied quantitatively, however, it will be found that the amido-acids combining in this manner with the hydrochloric acid of the gastric juice do give rise to some disturbance of proteolytic action;[110] _i. e._, digestion may be less rapid, especially on egg-albumin, a conclusion which Salkowski[111] has lately confirmed. Still, under such circumstances, digestion does go on and at a fairly rapid rate; hence, if there is a combination between the acid and these organic bodies, as is indicated by Günzburg’s reagent, the acid is still active physiologically, even more so than in the compound formed by the interaction of proteid and acid. In other words, many of these neutral organic bodies that may originate in the stomach through fermentative processes, or otherwise, and which tend to combine with the acid of the gastric juice, do not, as a rule, impede pepsin-proteolysis to the same extent that an excess of proteid matter may. In fact, in artificial digestions long continued, pepsin-acid solutions containing considerable leucin, for example, may accomplish as much in the way of digesting proteid matter as the same amount of pepsin-acid without leucin; but the inhibitory action of the amido-acid is there, and may be shown during the first few hours of the experiment, when less proteoses and peptones are formed than in the control experiment without leucin. [107] Le suc gastrique chez l’homme et les animaux, ses propriétés chimiques et biologiques. Paris, 1878. [108] Zeitschr. f. klin. Medicin, Band 14, Heft 1 and 2. [109] Ueber den Begriff der freien und gebundenen Salzsäure im Magensaft. Virchow’s Archiv, Band 122, p. 235. [110] Rosenheim: Centralbl. f. klin. Medicin, 1891, No. 39. F. A. Hofman, ibid., No. 42. [111] Ueber die Bindung der Salzsäure durch Amidosäuren. Virchow’s Archiv, Band 127, p. 501.