The hypophyseal substance—the synergic factor—which gives increased gonadotropic effects when combined with prolan has been shown to itself possess a definite though slight gonadotropic activity. It produces transitory follicular enlargement within 24–48 hours, which, however, regresses at once on cessation of treatment so that by the end of the 4th day the ovary again approximates its infantile weight.

The synergic principle indeed provokes only moderate ovarian development when administered in 100 times the dose necessary to demonstrate the activation phenomenon.

By means of isoelectric precipitation or by means of tryptic and ereptic digestion, fractions containing the synergic principle were freed of many contaminants, in particular of the antagonistic factor.

The synergic principle has been shown to be unaffected by digestion with trypsin or trypsin followed by a short digestion with erepsin, but the action of pepsin inactivated the material.

A preparation of the active substance has been obtained which is potent in a total dose of 27 gamma.

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