substances characteristic of the fluid secreted. Absorption of the products of digestion tends to increase the activity of the secreting cells, but we have no tangible proof that any particular kinds of food are directly peptogenous, i.e., that they lead to a storing up in the gastric cells, for example, of pepsinogen, although it may be that the so-called peptogenous foods give rise to a more active conversion of pepsinogen into pepsin.23 As already stated, the zymogen is manufactured directly from the cell-protoplasm, and the constructive power is certainly not directly controlled by the character of the food ingested.

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-wyssozki24 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, Podolinski26 claims that trypsin originates from its particular zymogen through a process of oxidation, and Herzen27 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 observer28 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.

It must be remembered, however, that in spite of oft-repeated attempts to obtain more definite knowledge regarding the composition of these proteolytic enzymes our efforts have been more or less baffled. We are confronted at the outset with the fact that no criterion of chemical purity exists, either in the way of chemical composition or of chemical reactions. The only standard of purity available is the intensity of proteolytic action, but this is so dependent upon attendant circumstances that it is only partially helpful in forming an estimate of chemical purity. My own experiments in this direction, and they have been quite numerous, have convinced me that it is practically impossible to obtain a preparation of either pepsin or trypsin at all active which does not show at least some proteid reactions. Furthermore, such samples of these two enzymes as I have analyzed have shown a composition closely akin to that of proteid bodies. I will not take time to go into all the details of my work in this direction, contenting myself here with the statement that the purest specimens of pepsin and trypsin I have been able to prepare have always shown their relationship to the proteid bodies by responding to many of the typical proteid reactions, and their composition, though somewhat variable, has in the main substantiated this evident relationship.

The most satisfactory method I have found for obtaining a comparatively pure preparation of pepsin, and one at the same time strongly active, is a modification of the method published some years ago by Kühne and myself.29 The mucous membrane from the cardiac portion of a pig’s stomach is dissected off and washed with water. The upper surface of the mucosa is then scraped with a knife until at least half of the membrane is removed. These scrapings, containing the fragments of the peptic glands, are warmed at 40° C. with an abundance of 0.2 per cent. hydrochloric acid for ten to twelve days in order to transform all of the convertible albuminous matter into peptone. The solution is then freed from insoluble matter by filtration and immediately saturated with ammonium sulphate, by which the pepsin, with some albumose, is precipitated in the form of a more or less gummy, or semi-adherent mass. This is filtered off, washed with a saturated solution of ammonium sulphate and then dissolved in 0.2 per cent. hydrochloric acid. The resultant solution is next dialyzed in running water until the ammonium salt is entirely removed, thymol being added to prevent putrefaction, after which the fluid is mixed with an equal volume of 0.4 per cent. hydrochloric acid and again warmed at 40° C. for several days. The ferment is then once more precipitated by saturation of the fluid with ammonium sulphate, the precipitate strained off, dissolved in 0.2 per cent. acid and again dialyzed in running water until the solution is entirely free from sulphate. The clear solution of the ferment obtained in this manner can then be concentrated at 40° C. in shallow dishes, and if desired the ferment obtained as a scaly residue. So prepared, the pepsin is certainly quite pure, that is comparatively, and although it may contain some albumose, the latter must be very resistant to the action of the ferment; indeed, pepsin is in many respects an albumose-like body itself.

In any event, the enzyme prepared in this manner shows decided proteid reactions, and contains nitrogen corresponding more or less closely to the recognized composition of an albumose. My own belief, therefore, is that these enzymes, both pepsin and trypsin, are proteid bodies