1. At equal hydrogen ion concentration the rate of pepsin digestion of gelatin, egg albumin, blood albumin, casein, and edestin is the same in solutions of hydrochloric, nitric, sulfuric, oxalic, citric, and phosphoric acids. Acetic acid diminishes the rate of digestion of all the proteins except gelatin.
2. There is no evidence of antagonistic salt action in the effect of acids on the pepsin digestion of proteins.
3. The state of aggregation of the protein, i.e. whether in solution or not, and the viscosity of the solution have no marked influence on the rate of digestion of the protein.