In 1895 Oliver and Schafer first demonstrated the action of posterior pituitary extracts on the vascular system. Since then preparations have been made which are suitable for clinical use, but the hormone or hormones of the posterior pituitary have not been isolated in chemically pure form. Some of the problems of the posterior pituitary must await the identification in chemically pure form of the "mother" substance of Abel,1 its fractional derivatives or separate fractions.2 The physiologic investigations of this gland have already far outstripped chemical studies. It seems likely, therefore, that chemical purification will merely settle the controversy that has existed as to whether a single hormone is responsible for the diverse physiologic actions of the posterior pituitary or whether at least three or more active principles exist as such and are transported as separate entities in the blood stream.
Not the least striking of the properties of