“…Suitable animals are the rabbit (Fitzpatrick, 1961), guinea-pig (Tindal & Yokoyama, 1962) and rat (Bisset, Clark, Haldar, Harris, Lewis & Rocha e Silva, 1967). It is possible to obtain greater sensitivity by giving injections directly into the arterial supply, so that the oxytocin reaches its site of action in higher concentrations (Fitzpatrick, 1961; Bisset et al, 1967). Other workers have used the mammary gland in vitro; a strip of tissue is suspended in an organ bath, and the increases in tension caused by oxytocin are recorded (Mendez-Bauer, Cabot & CaldeyroBarcia, 1960;Ryden & Sj6holm, 1962;Roca et al, 1972 between the application of oxytocin and the expulsion of droplets of milk is related to the concentration of hormone applied (Van Dongen & Hays, 1966).…”