ABSTRACT
In 1935 Barcroft, Flexner, Herkel, McCarthy & McClurkin, working on rabbits, showed that the oxygen saturation of the blood leaving the uterus dropped from an average value of about 70 % at the 18th day of gestation to about 30 % saturation on the 30th day. During the period in question the foetuses are in active growth, whilst growth of the placenta is only trifling. On the 18th day the combined weight of the foetuses is approximately the same as that of the foetal portions of the placentas to which they are attached; on the 30th day the foetuses weigh about fifteen times as much as the placentas.
It is right to say that one observation has.been omitted from this figure on the ground of its inherent unlikelihood, 92% saturation in a 25-day rabbit; apart from gross contamination with air, which is believed not to have taken place, the rupture of an artery might produce such a result.
