The period between 1825 and 1833 was characterized especially by the presentation of the many results bearing on gastric digestion obtained by Dr. Beaumont on Alexis St. Martin, followed a little later, in 1842, by a long period of experimentation by many physiologists, as Blondlot,[3] Bassow,[4] Bardeleben,[5] Bernard,[6] Bidder and Schmidt,[7] and many others on methods of establishing gastric fistulæ on animals, by which many interesting results were accumulated regarding the physiology of gastric digestion. Up to 1834, however, there was no adequate explanation offered of the solvent power of the stomach juice; aside from the presence of hydrochloric acid, nothing could be discovered by the earlier chemists to account for the remarkable digestive action. Eberle,[8] however, attributed to the mucous membrane of the stomach a catalytic action, and claimed that it only needed the presence of a small piece of the stomach mucosa with weak hydrochloric acid for the manifestation of solvent or digestive power. It remained for Schwann,[9] to show the true explanation of this phenomenon, and although he was unable to make a complete separation of the active principle which he plainly believed existed, he gave to it the name of pepsin. Wassmann, Pappenheim,[10] Valentin, and later Elsässer,[11] all endeavored to obtain the substance in a pure form, and Wassmann,[12] in 1839, surely succeeded in obtaining a very active preparation of the ferment--one capable of exerting marked digestive action when mixed with a little dilute acid. Thus, a true understanding of the general nature of gastric juice was finally arrived at, and the cause of its digestive power was rightfully attributed to the presence of the ferment pepsin and the dilute acid. Further, the analysis of human gastric juice made by Berzelius,[13] in 1834, showed that the secretion contains very little solid matter (1.26 per cent.), thus calling attention to the fact that the digestive power of this fluid is out of all proportion to the amount of pepsin, or even to the amount of total solid matter present, and consequently paving the way for a general appreciation of the peculiar nature of the dominant body, _i.e._, the pepsin. [3] Traité analytique de la Digestion. Paris, 1842. [4] Bulletin de la Société des Naturalistes de Moscou, vol. 16. 1842. [5] Archiv für physiol. Heilkunde, vol. 8. 1849. [6] Lecons de Physiologie de la Digestion. Paris, 1867. [7] Die Verdauungssäfte. [8] Physiologie der Verdauung. Würzburg, 1834. [9] Ueber das Wesen der Verdauungsprocesse. Müller’s Archiv, 1836, p. 90. [10] Zur Kenntniss d. Verdanuung. Breslau, 1839. [11] Magenerweichung der Säuglinge. Stuttgart und Tübingen, 1846. [12] Lehmann’s Lehrbuch d. physiol. Chem., Band 2, p. 41, 2te Auflage. [13] Lehrbuch der Chemie, Band 9, p. 209.