Insulin has been obtained in crystalline form from the islet of certain fishes. These crystals are identical in shape, in physiological activity and in sulphur content with those prepared from beef insulin.
In the crystallization of insulin from pig's pancreas difficulties have been encountered. Different reasons for these difficulties have been given. The crystalline material so far obtained differs in physiological activity and sulphur content from beef and fish insulin.
The physiological activity of crystalline beef insulin was found to be about 24 international units per milligram. This value is in good agreement with that found by other laboratories.
The preparation of crystalline insulin has been discussed. It has been pointed out that the nature of the commercial insulin preparation is of importance for obtaining readily a crystalline product.