Simultaneous intramammary pressure recordings were made on pectoral and inguinal mammary glands of the sow. Oxytocin was injected via the ear vein and the nature of the pressure curves resulting from quantities of hormone above physiological level studied. The frequency of the periodic contractions of the mammary myopethelium under these conditions was measured and compared with human uterine responses under similar conditions.

The writer is indebted to Professor H. McK. Carey of the National Women's Hospital, Auckland for the intrauterine pressure graph shown in Fig. 3. Acknowledgement is also made of the technical assistance given during the experiments by Mr E. D. O'Reilly.