1. Synthesis of plastein from the products of peptic hydrolysis of small quantities of egg albumin can be demonstrated with amorphous or crystalline pepsin.

2. Synthesis of plastein from the products of peptic hydrolysis of amorphous or crystalline insulin can be demonstrated with amorphous or crystalline pepsin.

3. The plastein synthesised by pepsin from the products of peptic hydrolysis of insulin is physiologically inactive.

4. The plastein formed in the insulin experiments could not be crystallised by the methods used for the crystallisation of insulin.

5. The physiological activity of insulin is not destroyed by repeated freezing (at about –50°C.) and melting of an aqueous or an alcoholic solution of this hormone.

6. No marked decrease in the physiological activity of insulin after incubation at 37°C. with pepsin at pH 4.0, in dilute or concentrated solutions, was detected.

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