Alkali Reserve of Normal, Pregnant, and Fetal Sheep *

In a study of the carbon dioxide exchange between the fetal and maternal bloods of goats, Keys' observed that the alkali reserve of the fetal blood sampled after caesarian section was higher than that of the maternal plasma obtained after the delivery of the fetus. The alkali reserve of the fetal kids fell within the range characteristic of normal barren goats, but that of the mother was in every case below the normal range. These observations, made on goats in the last 30 days of the gestation period, led him to infer that the pregnant goat is in a state of metabolic acidosis, an inference that gained support from studies by Barcroft and his collaborators' indicating that the position of the oxygen dissociation curve, prepared at constant CO2 pressure with the blood of gravid goats, was to the right of the field characteristic for the curves similarly prepared with blood from individuals not gravid. My own observations on the carbon dioxide content of fetal and maternal plasmas of sheep,2 drawn under similar circumstances after the lambs had been delivered by caesarian section, indicated that here, too, the concentration was higher in the fetal plasma. This observation, viewed in the light of the results of Keys' and Barcroft et al.,2 pointed to the possibility that the gravid ewe like the goat was in a state of metabolic acidosis. Hence, I determined to examine this possibility in the hope of learning something about the genesis and development of pregnancy acidosis. The results obtained form the substance of this report which deals with the alkali reserve in normal barren ewes, in gravid individuals at several stages in gestation, and fetuses in a number of different stages of development. As the first step in the investigation the alkali reserve was determined in a series of normal ewes that were not pregnant and had not recently been so, in an effort to establish the level and the range of variation characteristic of individuals kept under usual farm conditions. Those objectives obtained, I next followed the changes in the alkali reserve in a small series of ewes, with appropriate controls, before, during, and after the gestation period.