Page:Proceedings of the Royal Society of London Vol 60.djvu/48

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Recently, while exam ining specimens of ripe placentas for fatty degeneration, I was struck by th e regularity of the occurrence of fat in this structure, and especially by the n atu re and extent of its distribution. I was then led to examine a series of specimens taken at different periods of gestation, with the result th a t a free deposit of fat was found in ten different placentae, all of which I believe to be non-pathological; and ranging practically through all periods of gestation, from the sixth week up to term.

The method employed for the dem onstration of this fat, was to take slices from different parts of the placenta, and harden them for a few days in M uller s fluid; then to transfer thin strips, not exceeding oneth ird of an inch in thickness, to M archi’s fluid (1 per cent, solution of osmic acid 1 part, M uller’s fluid 2 parts) for a week. The pieces were then embedded in paraffin, cut with a rocking microtome, and stained lightly with saffranine, eosine, or logwood and eosine, or m ounted unstained. By this process the fat is completely blackened, while the other tissues retain th eir norm al staining reactions, so th at the outlines of the fat-containing cells can be distinctly made out.

By this method I have been able to dem onstrate the constant occurrence of fat in certain well-defined regions of the human placenta.

In the young hum an placenta, the epithelial covering of the villi consists of two layers, a superficial, nucleated, plasmodial layer, and a deep cellular layer. In a six weeks’ ovum I found fat in the form of minute droplets in both these layers, but much more abundantly in the former than in the latter. These fat droplets show com paratively little variation in size, and they remain discrete, showing little or no tendency to form larger droplets by fusion ; they are confined to the perinuclear protoplasm, and are never found in the nuclei, which remain unaltered in num ber, form, and arrangem ent. The strom a of these villi contains here and there a trace of fat, but it is apparently healthy, and is furnished w ith well-formed wide capillaries filled with blood. The villi are, in fact, to all appearance healthy. Every villus does not show this deposit of fat, but- it is present in very large numbers of th e m ; in every field of the microscope several villi