All this in one sense is to-day ancient history, but I recall it to your minds in order to emphasize the fact that these two energetic ferments or enzymes stand in close relation to the protoplasm of the cell from which they originate. So far as we can measure the transformations involved, there are only two distinct steps in the process, viz., the formation of the inactive zymogen stored up in the cell, and the conversion of the antecedent body into the soluble and active ferment. In this connection Pod-wyssozki[24] has reported that the mucous membrane of the stomach exposed to the action of oxygen gas shows a marked increase in the amount of pepsin, from which he infers that the natural conversion of pepsinogen into pepsin is an oxidation process. Further, he claims the existence of at least two forms of pepsinogen in the stomach mucosa, one closely akin to the ferment itself and very easily soluble in glycerin, while the other is more insoluble in this menstruum. Langley and Edkins,[25] however, find that oxygen has no effect whatever on the pepsinogen of the frog’s mucous membrane, thus throwing doubt on the above conclusion. Still, Podolinski[26] claims that trypsin originates from its particular zymogen through a process of oxidation, and Herzen[27] has proved that the ferment can be reconverted into trypsinogen under the influence of carbon-monoxide and again transformed into the ferment by contact with oxygen gas. This latter observer[28] has also noticed a connection between the amount of trypsin obtainable from the pancreas and the dilatation of the spleen, from which he was eventually led to conclude that the spleen during its dilatation gives birth to a zymogen-transforming ferment which thus leads to the production of trypsin, presumably from the already manufactured zymogen. In any event, their peculiar origin lends favor to the view that these two enzymes are closely allied to proteid bodies, and that they are directly derived from the albuminous portion of the cell-protoplasm. Analysis shows that they always contain nitrogen in fairly large amount, although the percentage is sometimes less than that found in a typical proteid body. [24] Pflüger’s Archiv f. Physiol., Band 39, p. 68. [25] Journal of Physiol., vol. 7, p. 400. [26] Pflüger’s Archiv f. Physiol., Band 13, p. 422. [27] Ueber den Rückschlag des Trypsins zu Zymogen unter dem Einfluss der Kohlenoxydvergiftungen. Pflüger’s Archiv f. Physiol., Band 30, p. 308. [28] Ueber den Einfluss der Milz auf die Bildung des Trypsins. Pflüger’s Archiv f. Physiol., Band 30, p. 295.