Pregnancy in women has been shown by Boyd (1) to be accompanied by a lipemia involving certain definite changes in the lipid concentration of the red blood cells and blood plasma. Correlating this with earlier work the conclusion was reached that the increase in the concentration of blood lipids commences about midway in the nine months of gestation. Fat metabolism in the fetus also becomes active about the mid-point of pregnancy as indicated by increasing amounts of lipids being laid down in the growing offspring (2). The time relationship of these two processes suggests that they may be related.To prove or disprove this possible relation was the purpose of the present investigation. As a working hypothesis it was suggested that as the lipid concentration in the maternal blood stream increases, the placenta passes more of these substances on to umbilical blood from whence they are absorbed in increasing amounts by the fetus. This theory requires proof (a) that lipids are absorbed from umbilical blood by the fetus, and (b) that lipids are added to umbilical blood by the placenta. The placenta of the rabbit and rat has been shown in recent years to be "permeable" to lipids by Bickenbach and Rupp (14), Sinclair (15) and Chaikoff and Robinson (16). By analogy the human placenta has been assumed to be "permeable" also. Direct proof of the " permeability " of the human placenta to lipids is lacking and it should be recalled that the structure of the human placenta differs from that of the rat and the rabbit. In fact Slemons and Stander (3) and many others as reviewed by Needham (2), Mayer (4), Schlossmann (5), etc., believe that the human placenta does not permit the passage of fats to the fetal circulation because they found that the lipid concentration of blood on the maternal side of the placenta was always higher than

Del~art.tti.cht of Obstetrics andGywcology n?nd the Dqmrtntriit of Anatomy of the Uaiz:or&g of Xochester TWO PLATES (SEVEN FIGURES) INTHOnUCTION The studies of St ockard aiid Papariicolaou 011 the guineapig ( '17) aiicl of Long and 'E;rans on the rat ('22) showed in a most striking manner the definite cyclic changes occurring in tlic vaginal miicosa of these rodents and their relation to the oestrons cycle. Since the appearance of these works, a iiumber of other observers have studied the vaginal smears of other spccics in an effort to correlate the variations found in the ~agilial secretions with the various phases of the oestrous cycle. Thus, Allen ( '22) foiind in the white monse a series of cyclic changes quite similar to those described by Long aiid Evans in the rat, both iii tho vaginal smears as well as in the histological appearance of tlic vaginal mucosa. Hartman ( '23), studying the opossum, also fo1111tl ~ariatioiis in the cell content of the vaginal smears and variations in the histological appearance of the vaginal mucosn at different phases of the oestrons cycle. I n all of these species the variatioas noted were very sharply defined. I n Macacus rhesns, 011 the other hand, Corner ( '23) found irregular variations in the iiiimber of epithelial cells and Ieucocyt es found in the vaginal smears. Observations by Murphey ( '22) in the ox and by Zupp ('24) in the sow also showed variations in the leucocyte and epithelial cell content of the vagiiial smears at different periods of the oestrons 417

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