title="13"/> closely related to the albumoses. They are soluble in water and more or less soluble in glycerin; at least glycerin will dissolve them from moist tissues, or from moist precipitates containing them. Langley,30 however, states, and perhaps justly, that we have no positive proof that either ferments or zymogens are soluble in pure strong glycerin, and that if they are soluble, it is extremely slowly. In dilute glycerin, however, these ferments dissolve readily, as we very well know. Furthermore, they are practically non-diffusible, and, like many albumoses, are precipitated in part by saturation with sodium chloride and completely on saturation with ammonium sulphate.

When dissolved in water and heated above 80° C., these enzymes are decomposed to such an extent that their proteolytic power is totally destroyed. The amount of coagulum produced by heat, however, is comparatively small, though variable with different preparations. Thus with trypsin, Kühne originally considered that boiling an aqueous solution of the ferment would give rise to about twenty per cent. of coagulated proteid and eighty per cent. of peptone-like matter. With the purer preparations now obtainable there is apparently less coagulable matter present, and Loew31 has succeeded in preparing from the pancreas of the ox a sample of trypsin containing 52.75 per cent. of carbon and 16.55 per cent. of nitrogen, and yielding only a small coagulum by heat. Loew considered the ferment to be a true peptone, but in view of our present knowledge regarding the albumoses, I think we are justified in assuming it to be an albumose-like body rather than a true peptone. At the same time it may be well to again emphasize the fact that our only “means of determining the presence of an enzyme is that of ascertaining the change which it is able to bring about in other substances, and since the activity of the enzymes is extra­ordinarily great, a minute trace suffices to produce a marked effect. From this it follows that the purified enzymes which give distinct proteid reactions might merely consist of very small quantities of a true non-proteid enzyme, adherent to or mixed with a residue of inert proteid material.”32 This quotation gives expression to a possibility which we certainly cannot ignore, but my own experiments lead me to believe firmly in the proteid nature of these two enzymes. Further, we find partial substantiation of this view in the results obtained by Wurtz33 in his study of the vegetable proteolytic ferment papain, and in my own results from the study of the proteolytic ferment of pineapple juice.34 Thus, Wurtz prepared from the juice of Carica papaya an active sample of papain, and found it to contain on analysis about 16.7 per cent. of nitrogen and 52.5 per cent. of carbon, while the reactions of the product likewise testified to the proteid nature of the enzyme. Martin, too, has concluded from his study of papain that the ferment is at least associated with an albumose.35

With the proteolytic ferment of pineapple juice my observations have led me to the following conclusions, viz., that the ferment is at least associated with a proteid body, more or less completely precipitable from a neutral solution by saturation with ammonium sulphate, sodium chloride, and magnesium sulphate. This body is soluble in water, and consequently is not precipitated by dialysis. It is further non-coagulable by long contact with strong alcohol, and its aqueous solution is very incompletely precipitated by heat. Placing it in line with the known forms of albuminous bodies it is not far removed from protoalbumose or heteroalbumose, differing, however, from the latter in that it is soluble in water without the addition of sodium chloride. At the same time, it fails to show some of the typical albumose reactions, and verges toward the group of globulins. In any event, it shows many characteristic proteid reactions, and contains considerable nitrogen, viz., 10.46 per cent., with 50.7 per cent, of carbon. Consequently, we may conclude that the chemical reactions and composition of the more typical proteolytic enzymes, both of animal and vegetable origin, all favor the view that they are proteid bodies not far removed from the albuminous matter of the cell-protoplasm.

Further, the very nature of these substances and their mode of action strengthen the idea that they are not only derived from the albumin of the cell-protoplasm, but that they are closely related to it. One cannot fail to be impressed with the resemblance in functional power between the unformed ferments as a class and cell-protoplasm. To what can we ascribe the particular functional power of each individual ferment? Why, for example, does pepsin act on proteid matter only in the presence of acid, and trypsin to advantage only in the presence of alkalies? Why does pepsin act only on proteid matter, and ptyalin only on starch and dextrins? Why does trypsin produce a different set of soluble products in the digestion of albumin than pepsin does? Similarly, why is it that the cell-protoplasm of one class of cells gives rise to one variety of katabolic products, while the protoplasm of another class of cells, as in a different tissue or organ, manifests its activity along totally different lines? The answer to both sets of questions is, I think, to be found in the chemical constitution of the cell-protoplasm on the one hand, and in the constitution of the individual enzymes on the other. The varied functional power of the ferment is a heritage from the cell-protoplasm, and, as I have said, is suggestive of a close relationship between the enzymes and the living protoplasm from which they originate. We might, on purely theoretical grounds, consider that these unformed ferments are isomeric bodies all derived from different modifications of albumin and with a common general structure, but with individual differences due to the extent of the hypothetical polymerization which attends their formation.

Whenever, owing to any cause, the activity of the ferment is destroyed, as when it is altered by heat, strong acids, or alkalies, then the death of the ferment is to be attributed to a change in its constitution; the atoms in the molecule are rearranged, and as a result the peculiar ferment power is lost forever. The proteolytic power of these enzymes is therefore bound up in the chemical constitution of the bodies, and anything which tends to alter the latter immediately interferes with their proteolytic action. But how shall we explain the normal action of these peculiar bodies? Intensely active, capable in themselves of producing changes in large