Abstract
I. INTRODUCTION It is generally conceded that intravenous injections of the extract of the infundibular portion of the pituitary gland cause a rise in blood-pressure ; that this rise is due to a peripheral constriction of blood-vessels, and that when repeated injections are made, the rise in pressure diminishes with each injection until a fall in pressure occurs. This change in the effect of repeatedly administered injections of pituitary extracts is designated as its "depressor action." No attempt will be made here to cover with detailed references the previous work on this subject, which is readily accessible in a recent article by Wiggers.1 A brief summary of the commonly accepted interpretation of these results seems, however, necessary. In 1899 Schäfer and Vincent2 suggested that extracts of the pituitary gland contained two substances, one having a pressor, the other a depressor effect, the former inducing a constriction

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