Native Proteid.
Syntonin.
Protoproteose.Heteroproteose.
(dysproteose).
Deuteroproteose.Deuteroproteose.
Peptone.Peptone.

It is, of course, to be understood that this is not intended to represent anything more than the order of formation of the several bodies, no attention being paid here to the hemi- or anti-character of the several products, or classes of products. Thus, proto and heteroproteose are primary bodies formed directly from the initial product syntonin by the further action of the ferment. In the same sense, deutero­proteose is a secondary proteose, being formed by the further hydration of the primary body. Lastly, peptones, the final products of pepsin-proteolysis, are the result of the hydration and possible cleavage of deutero­proteoses. Further, in almost every gastric digestion there is also formed a small amount of antialbumid, a product insoluble in dilute hydrochloric acid and which consequently appears as an insoluble residue. This body is very resistant to the action of pepsin-acid when once formed, but may be slowly converted, in part at least, into a soluble antialbumose and thence into antipeptone.

All of these bodies can be readily identified in any digestive mixture containing them by a few simple reactions. Thus, after having removed any acid-albumin or syntonin present by neutralization, the concentrated fluid can be tested at once. If primary proteoses are present, the neutral fluid will yield a more or less heavy precipitate on addition of crystals of rock-salt, precipitation being complete only when the fluid is saturated with the salt. Further, if the proteoses are present in not too small quantity, nitric acid added drop by drop to the neutralized fluid will produce a white precipitate, readily soluble on application of heat but reappearing as the solution cools. If primary proteoses are wholly wanting, then no precipitate will be obtained by acid unless the fluid is saturated with salt, in which case a portion of the deutero­proteose will be precipitated. The two primary proteoses differ from each other especially in solubility; protoproteose being readily soluble in water alone, while heteroproteose is soluble only in salt solutions, dilute acids, and alkalies. Hence, when these two bodies are precipitated together by saturation with salt, they may be readily separated by dissolving them in a little dilute salt solution, and dialyzing the fluid in running water until the salt is entirely removed; heteroproteose will then be precipitated, while the proto-body remains in solution.

By long contact with water, and even with concentrated salt solutions, heteroproteose tends to undergo change into a semi-coagulated form, named dysproteose, insoluble in dilute sodium-chloride solutions. This body can be reconverted into heteroproteose, in part at least, by solution in dilute acid, or alkali, and reprecipi­tation by neutralization.

As a class, the proteoses are characterized by far readier solubility in water than native proteids, by a far greater degree of diffusibility, by non-coagulability by heat and by alcohol, although precipitable by the latter agent. Further, nearly all proteose precipitates are exceedingly sensitive toward heat, tending to dissolve as the fluid is warmed and reappearing as the solution cools. In fact, this peculiarity often serves as a means of identification. Potassium ferrocyanide and acetic acid, picric acid in excess, and likewise cupric sulphate, all precipitate the primary proteoses, while deutero­proteose is only slightly affected by these reagents, or indeed not at all.

In order to separate the secondary proteose from the primary bodies in the absence of peptones, the fluid is neutralized as nearly as possible, and then, after suitable concentration, is saturated with sodium chloride for the partial precipitation of the primary proteoses. To the clear filtrate, acetic acid[117] is added drop by drop as long as a precipitate results, the latter being composed of a mixture of protoproteose and deutero­proteose. That is to say, protoproteoses are not completely precipitated from neutral solutions by saturation with salt alone; a little acid is required to complete it, but this tends to bring down a certain amount of deutero­proteose. From this filtrate, however, the deutero-body can be separated in a pure form by dialyzing away the salt and acid, and then concentrating the fluid and precipitating with alcohol. When the proteoses are mixed with peptones, the former must first be separated collectively by saturation of the fluid with ammonium sulphate.

Peptones are especially characterized by non-precipitation with the ordinary precipitants for proteid bodies, and especially by the fact that they are wholly indifferent to saturation with ammonium sulphate either in neutral, acid, or alkaline fluids. This reaction, which constitutes the main, and perhaps the only absolute method of separating peptones from proteoses must be carried out with great thoroughness in order to insure a complete precipitation of deutero­proteose. The latter stands midway between primary proteoses and peptones in many respects, and seems to share with peptones something of a tendency to resist precipitation by the ammonium salt. Indeed, as Kühne[118] has recently pointed out, the last traces of deutero­proteose can be precipitated from the fluid only by long continued boiling of the ammonium sulphate-saturated fluid, and even then it is seldom complete unless the reaction of the fluid is alternately made neutral, acid, and alkaline, and the heating continued for some time after each change in reaction. Under such circumstances, the last portions of deutero­proteose separate from the salt-saturated fluid and float on the surface in the form of an oily or gummy mass, while the true peptone remains in the fluid absolutely non-precipitable by the salt.

In this filtrate, peptone can be detected by adding to a small portion of the fluid a very large excess of a strong solution of potassium hydroxide, followed by the addition of a few drops of a very dilute solution of cupric sulphate. If peptone is present a bright red color will appear, the intensity of which, with the proper amount of cupric sulphate, will be proportional to the amount of peptone present. If it is desired to separate the peptone from the ammonium-sulphate-saturated fluid, there are several methods available, of which the following is perhaps the most satisfactory: The fluid is concentrated somewhat, and set aside in a cool place for crystal­liza­tion of a portion of the ammonium salt. The fluid is then mixed with about one-fifth its volume of alcohol, and allowed to stand for some time, when it separates into two layers—an upper one, rich in alcohol, and a lower one, rich in salts. The latter is again treated with alcohol, by which another separation of the same order is accomplished. Finally, the lighter alcoholic layers containing the peptone are united, and exposed to a low temperature until considerable of the contained salt crystallizes out. The fluid is then concentrated, and after addition of a little water is boiled with barium carbonate until the fluid is entirely free from ammonium sulphate. Any excess of baryta in the filtrate is removed by cautious addition of dilute sulphuric acid, after which the concentrated fluid, reduced almost to a sirupy mass, is poured into absolute alcohol for precipitation of the peptone.

So separated, the peptone formed in gastric digestion is exceedingly gummy, but can be transformed into a yellowish powder, very hygroscopic, of more or less bitter taste, and, when thoroughly dry, dissolving in water with a hissing sound and with considerable development of heat, like phosphoric anhydride.[119]