Peptones, _i. e._, amphopeptones, are the final products of gastric digestion; but to how great an extent is actual peptonization carried on in pepsin-proteolysis? As we have seen, syntonin, primary proteoses, secondary proteoses, and peptones are all products of pepsin-digestion, and it might perhaps be assumed that ultimately all of a given proteid undergoing pepsin-proteolysis would be converted into amphopeptone. Examination, however, shows that such is not the case, at least in artificial digestive experiments. Peptones are truly formed, and many times in large amount, but never under any circumstances have I been able to effect a complete transformation of any proteid into true peptone by pepsin-proteolysis; there is always found a certain amount of proteoses more or less resistant to the further action of the ferment. Obviously, the nature and proportion of the individual products formed in any digestive experiment are dependent greatly upon the attendant conditions; but even with a large amount of active ferment, an abundance of free hydrochloric acid, a proper temperature, and a long-continued period of digestion, even five and six days, there is never found a complete conversion into peptone. Indeed, the largest yield of peptone I have ever obtained in an artificial digestion is sixty per cent., while the average of a large number of results under most favorable circumstances is somewhat less than fifty per cent.[139] [139] Chittenden and Hartwell: The Relative Formation of Proteoses and Peptones in Gastric Digestion. Journal of Physiol., vol. xii, p. 12. We understand that peptones are the products of the hydration and cleavage of previously formed proteoses. The primary proteoses pass into secondary proteoses and these into peptones, but for some reason this transformation after a time becomes a slow and gradual process. At first there is a marked and rapid progression; the proteid undergoing proteolysis is rapidly dissolved, and both proteoses and peptones may be detected in abundance. But if we continue to watch the changing relations of primary and secondary proteoses and peptones, we find that progression soon ceases to be rapid, and eventually travels onward at a snail’s pace. Thus, in one experiment with coagulated egg-albumin, there was found at the end of forty-eight hours’ digestion with pepsin-hydrochloric acid, only thirty-seven per cent. of peptones with fifty-eight per cent. of proteoses, and yet digestion had been sufficiently vigorous to allow of a complete solution of the proteid in two hours. At the end of seventy-two hours the amount of peptones had increased to about forty-two per cent., the proteoses having correspondingly diminished; but even at the end of seventeen days only fifty-four per cent. of peptones were to be found, thus affording striking evidence of the slow conversion of the first-formed products into peptones.