"Crystalline insulin" was released for general sale in August 1938 under the name "insulin specially prepared as solution of zinc insulin crystals." However, in contrast to the other two types of insulin now commercially available, the regular type (amorphous, unmodified) and the protamine zinc insulin, its rapidity of action and duration of effect have remained controversial. In the hope of clarifying the issue, in November 1938 we undertook a comparison of the action of regular insulin (prepared from amorphous material) with that of solution of zinc insulin crystals and now present the results of the study.
In 1926 Abel1 and his associates succeeded in obtaining insulin in crystalline form from highly purified amorphous preparations. Scott2 in 1934 noted that samples of such crystalline preparations contained traces of zinc; he observed also that crystals were formed only in the presence of certain heavy metals—zinc, nickel, cobalt or cadmium. By
MARBLE A, VARTIAINEN I. CRYSTALLINE INSULIN. JAMA. 1939;113(14):1303–1309. doi:10.1001/jama.1939.02800390025007
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