Page:Proceedings of the Royal Society of London Vol 60.djvu/49

Rh containing fat may be found. The am ount of fat also varies considerably.

In a young ovum the plasm odial layer of the villi shows g re at p ro ­ liferative activ ity ; it throw s out num erous club-shaped processes or buds, which represent the first stage in th e developm ent of new villi. These buds very frequently contain large num bers of m inute fat droplets. 1 believe th at this is a point of very great im portance, showing, as it does, th a t the deposit of fa t occurs in actively grow ing tissues of undoubted vitality.

In the ripe placenta the proliferation of th e plasm odial layer has ceased, and degenerative changes are present in scattered regions. But, of course, the great m ajority of th e villi retain th eir vitality, and in these villi a free deposit of fat is present, showing the same distribution and characters as in th e young placenta.

I have also found a sim ilar deposit of fat in the serotina. The six weeks’ ovum, above referred to, showed very m any decidual cells containing m inute, discrete droplets of fat in the perinuclear protoplasm. " A placenta of the sixth month also showed an abundant fat deposit in the same region. A t term, the serotina shows m any degenerative changes, and although it contains fat, it may well be doubted whether, at this period, this is a physiological deposit.

The placenta, indeed, appears to be a storehouse of n utritive fat, ju st as is the liver. This appears to throw some light on w hat has long been one of the problem s of foetal physiology, viz., the source from which the foetus obtains its supplies of fat. Diffusible substances such as sugar, salts, peptones, &c., were supposed to pass by osmosis from the m aternal blood in the inter-villous spaces, to the foetal blood in the villi. B ut this could not be assumed of indiffusible substances such as fat. The tru th would seem to be th a t fat is deposited from the m aternal blood in the epithelium of the villi, and stored up there by the foetal tissues for their use. No great accum ulation of fat occurs, as it appears to be from tim e to tim e absorbed and disposed of by the foetal circulation. I t is, however, not altogether clear how a deposit of fat in the decidual cells can be made available for the purposes of foetal nutrition.

Since finding this fat deposit in the hum an placenta, I have begun a series of comparative observations upon the placentae of other mammals. Up to the time of w riting, I have examined two rabbits’ placentae, one from an early, and the other from a late, period of gestation. In both there was a m arked deposit of fat, chiefly in the superficial glandular layer of the m aternal placenta, but also, though to a less extent, in the processes of the chorionic mesoblast, which form the homologues of the villi of the hum an placenta.

The process appears to correspond closely to that observed by Mr. George Brook, in the transmission of fat from the yolk to