I n an earlier study (Corey, '32) an attempt was made to ascertain the fetal heart rate, blood velocity and blood pressure in the albino rat during the latter half of the gestation period. The maternal heart rate was determined by palpation, and that of the fetus by direct observation. Following this work it seemed desirable that a more detailed investigation be made of the physiology of the fetal heart by means of an improved technique and the analysis of kymographic records. Tracings of fetal heart action have now been secured by a very delicate suspension method, the operative procedure involving an imperceptible amount of hemorrhage. Synchronous tracings of maternal cardiac activity were obtained, wherever pertinent, by means of a needle thrust into the wall of the ventricle and suitably connected with a recording lever.
The regularity of the fetal heart beat served as an index of the normality of the animals observed, since even slight asphyxia (partial separation of the placenta, or strangulation of the cord) was found to result in a markedly irregular cardiac rhythm characterized by successive periods of acceleration and retardation. Fetuses exhibiting such abnormal heart action were discarded. Cardiac tracings were secured from 230 fetuses averaging 31 mm. in crown-rump length, and comprising sixty-one litters. Records were also secured from 127