CRYSTALLINE PEPSIN

Within a comparatively few months the successive announcements of the isolation of crystalline insulin, crystalline tuberculin, crystalline urease and crystalline pepsin have followed one another. It is not a long time, measured in terms of individual human experience, since the respiratory blood pigment oxyhemoglobin and the protein of aleurone grains in plants were cited as the only albuminous compounds readily demonstrable in crystalline form. Students of the chemistry of the proteins were continually being reminded of the unsatisfactory physical character of the materials they were investigating. Instead of beautifully crystallized products such as engrossed the attention of most of the inorganic and many of the organic chemists, the proteins then isolated appeared as amorphous substances, often difficult of solution, colloidal in behavior, and bearing few earmarks of the degree of purity exhibited by the crystalline products. Gradually there came progress in the isolation and purification of proteins; egg and serum