Some Recent Research on the Heart and Circulation

A BRANCH of physiology which has recently had much attention is fcetal physiology. In choosing to start with the fcetus, then, it is because it is convenient to do so, though I cannot deny that I am proud to say that the work formed the subject of the John Mallet Purser Lecture, Trinity College, Dublin, given last year by my father.l The foetuses used for the investigations were lambs or kids of known intrauterine age. They were removed from the mother by Caesarean section. A very important point was that after delivery they wvere placed in a bath of warm saline and the cord was not tied. For this reason the foetus continued to get its oxygen from the placental circulation and did not breathe. At any desired moment it could be "born" by tying the cord; breathing ensued after a pause of rather less than a minutc. At the risk of too much digression, I might mention that the essential stimulus for foetal respiration was found to be oxygen lack; carbon dioxide accumulation, per se, was ineffective. The following data may be taken as typical of the carotid arterial pressure of foetal sheep of different intrauterine ages, full term in the sheep being about 140 days: Fcetal age in days-During the last six weeks of pregnancy the fretal arterial pressure was doubled. The arterial pressure at full term, about 75 mm. Hg., is, however, very different from that of the newborn lamb. After "birth," that is, ligature of the cord, the pressure rises another 20 mm. Hg. at about the same time as breathing starts, so the pressure in the newborn lamb is about 100 mm. Hg. It is interesting to observe that the stage of development of the blood-pressure at birth is more advanced in