ioi4 A MANUAL OF PHYSIOLOGY 



the maternal portion of the placenta, but it is possible that the 

 villi also possess the power of haemolyzing intact corpuscles in the 

 circulating placental blood. Iron can be demonstrated by micro- 

 chemical reactions in the epithelial cells of the chorionic villi as fine 

 granules, which increase in size towards the base of the cells. As we 

 pass deeper into the villus towards its central bloodvessel, the granules 

 again diminish in size. The picture is very like that seen in the ab- 

 sorption of iron from the intestine. And if the microchemical picture 

 is practically the same, the process by which the iron is absorbed is 

 not likely to be fundamentally different in the two cases (p. 417). 



The same is true of the passage of fat across the placenta. Fat 

 can always be demonstrated microchemically in the chorionic villi. 

 The most superficial layer of the villi is free from visible fat droplets. 

 They increase in number towards the base of the epithelial cells. 

 As in the case of the intestine, these appearances agree well with 

 the view that the fat is split before being absorbed by the villi, and 

 undergoes resynthesis in the epithelium. That, as a matter of fact, 

 fat passes from the mother to the foetus is shown by the observation 

 that when pregnant guinea-pigs were fed with a foreign fat (from 

 cocoanuts), the characteristic fatty acid (lauric acid) was found in 

 the foetus. This, however, does not exclude the possibility that the 

 foetus may form fat in its own tissues from carbo-hydrates, and 

 perhaps from proteins, as it is destined to do in extra-uterine life. 



Among the carbo-hydrates the passage of dextrose from the 

 maternal to the foetal blood has been experimentally demonstrated. 

 A specially interesting proof is afforded in cases where the mother 

 suffers from diabetes mellitus. In one case in which the mother, 

 during diabetic coma, was delivered of a stillborn child, the blood 

 ;>f the child contained 2 '2 per cent, of sugar, its urine 5^24 per cent., 

 and the amniotic fluid 0*47 per cent. The blood of the mother had 

 a sugar content of o - 8 per cent., and her urine a content of 6^94 per 

 cent. The sugar of the maternal blood is not the only source of the 

 carbo-hydrates of the foetus. The glycogen store of the placenta is 

 to be regarded as a second source, which is rendered available on 

 conversion into dextrose by the placental diastatic ferment. This 

 store of easily available food material is especially important in the 

 early stages of development of the ovum before a circulation has 

 been established in the villi. In the youngest ova investigated the 

 decidual covering has been found rich in glycogen. 



While it is to be supposed that the products of the hydrolytic 

 decomposition of proteins can be absorbed by the foetal blood in its 

 passage through the placenta, to be synthesized to the appropriate 

 tissue proteins in the foetal organs, there is evidence that certain 

 proteins can be taken up without change. In this connection it 

 must be remembered that the mother is much more closely related 

 to the foetus as regards her protein composition than any ordinary 

 protein food can be to an animal in extra-uterine life. In some 

 respects, indeed, the foetus may be considered, especially, perhaps, 

 in the first stages of its development, as a part of the mother, an 

 additional, although very complex, organ rather than an independent 

 organism. 



The blood of the umbilical artery, although far from the level of 

 the ordinary arterial blood of the mother as regards its gaseous 

 content, is yet the best the foetus ever gets ; and by a series of con- 

 trivances it is assured that this best should go first to the most 

 important parts the liver, the heart, and the head while the legs 



