In pepsin-proteolysis we have to deal, in my opinion, with a series of progressive hydrolytic changes in which peptones are the final products of the transformation. Commencing with the formation of acid-albumin or syntonin, hydrolysis and cleavage proceed hand in hand, under the guiding influence of the proteolytic enzyme, and each onward step in the process is marked by the appearance of a new body corresponding to the extent of the hydrolysis; each body, perhaps, being represented by a row or series of isomers, all externally alike, but different in their inner structure, according to the proportion of hemi- and anti-groups contained in the molecule. As opposed to this theory, we have the older views of Maly,[120] Herth,[121] Henninger[122] and others, based upon observations which tend to show that peptones do not differ in chemical composition from the proteids which yield them. As a matter of fact, the products then analyzed were not peptones at all; they were merely the _primary_ products of pepsin-proteolysis, _i. e._, what we now term primary proteoses, and it is time we stopped using such data to enforce the theory that peptones are polymers of the proteids from which they are derived. [120] Ueber die chemische Zusammensetzung und physiologische Bedeutung der Peptone. Pflüger’s Archiv f. Physiol., Band 9, p. 585. [121] Ueber die chemische Natur des Peptones und sein Verhältniss zum Eiweiss. Zeitschr. f. physiol. chem., Band 1, p. 277. [122] De la Nature et du rôle physiologique des peptones. Paris, 1878. In 1886, the writer, in conjunction with Professor Kühne, commenced a study of the various cleavage products[123] formed by the action of pepsin-hydrochloric acid from the better characterized and purer proteids, this being a continuation of our earlier work on the proteoses and peptones formed from blood-fibrin, serum-albumin, etc. This work I have continued in my laboratory up to the present time, with many co-workers, and as a result we have to-day a series of observations gradually accumulated during these last seven years, some the results of work carried on this last year, which speak in no uncertain way of the character of both the primary and secondary products of pepsin-proteolysis. Furthermore, in attempting to settle this question once for all, I have selected for study examples from the various classes of both animal and vegetable proteids; and as representatives of the latter have had carried out two lengthy series of experiments on the crystallized proteids which occur so abundantly in some seeds, on the assumption that these crystalline bodies would furnish a certain guarantee of purity which might naturally be lacking in the amorphous proteids of animal origin. Some of these results are now placed together in the following tables, a study of which reveals some very interesting facts: [123] Globulin and Globuloses. Studies in Physiol. Chem. Yale University, vol. ii., p. 1.