These facts at once raise the question whether the products of proteolysis may not have a stronger affinity for acid than the native proteids; an affinity so strong that they may be able to withdraw acid from the acid-albumin first formed. One of our conceptions regarding pepsin-proteolysis is that acid is necessary for every step in the proteolytic process. A primary albumose, for example, cannot be further changed by pepsin, unless there is acid present for it to combine with. This being true, it is clear, in view of the fact that even peptones may appear in a digestive mixture containing an amount of acid insufficient to combine even with the albumin present, that the products of proteolysis must withdraw acid from the acid-albumin first formed. In regard to the first point, my own experiments certainly tend to show that the products of gastric digestion do combine with larger amounts of hydrochloric acid than undigested proteids; and further, that of the several products of proteolysis, the secondary proteoses combine with a larger percentage of acid than the primary proteoses, while true peptones combine with still larger amounts. In other words, the simpler and more soluble the proteid, the larger the amount of acid it is capable of combining with; a statement which accords with results obtained by other workers[101] in this direction. Further, another factor of considerable importance in connection with the natural digestive process is that a dissolved proteid, such as protoalbumose for example, will combine more readily with free acid than an insoluble proteid; from which Gillespie[102] is led to infer that in pepsin-proteolysis where there is no free acid present, only acid-albumin, proteoses may be formed to a limited extent at the expense of some of the acid of the acid-albumin, a portion of the latter being perhaps reconverted into albumin. The ability of the proteoses, however, to withdraw acid from its combination with a native proteid is perhaps best indicated by Kossler’s[103] experiments, which show that a solution of acid-albumin containing only enough hydrochloric acid to hold the albumin dissolved, on being warmed at 40° C. for some hours with addition of a neutral solution of pepsin, may undergo partial conversion into albumose or peptone. [101] See especially Gillespie: Gastric Digestion of Proteids. Journal of Anat. and Physiol., vol. 27, p. 207. [102] Loc. cit. [103] Beiträge zur Methodik der quantitativen Salzsäurebestimmung im Mageninhalt. Zeitschr. f. physiol. Chem., Band 17, p. 93.