438 Mr. Lawson Tait on the 



gitation, it will be found impossible to force the fluid into the substance 

 of the placenta. It is limited by a membrane, derived from the inner 

 layer of the chorion, into which the arteries pass to be included between 

 two layers of it, and from between which two layers the veins emerge. 

 This membrane is very tough ; and if extreme pressure be used the fluid 

 will be found to pass under the ligature and down the column which is 

 being injected, or by rupture into one of the other columns, but never, 

 accordiug to my experiments, can it be made to pass through that mem- 

 brane. There is absolutely no connexion, therefore, between the nutri- 

 tive system of the cord and that of the placenta. 



The amnion is loosely attached over the placenta by some cellular 

 tissue, which Arthur Farre describes as the tunica media. But the 

 amnion becomes adherent to the cord a few lines on the f cetal side of the 

 basis membrane of the placenta. 



The relations of this attachment have yet to be made out. 



VI. Its Nutrition. 



From what I have already said it will be apparent that I regard the 

 chief factor in the nutrition of the cord to be the capillary arrangements 

 at its foetal insertion, at which point the cord grows and obtains its 

 spiral form, and from which also it derives its supply of wandering cells. 

 From the facts observed in cases of extra-uterine gestation, however, it 

 has seemed to me to be likely that the stomata on the epithelial surface 

 of the cord also play an important part in its nutrition. The liquor 

 amnii contains casein, creatin, lactic acid, grape-sugar, and some saline 

 matter, all of which are very suggestive that the fluid is used for the 

 purposes of nutrition, and perhaps for that of the cord. In recent 

 cases of extra-uterine f oetation, before the liquor amnii becomes absorbed, 

 the cord remains fresh and plump. After the liquor amnii has become 

 absorbed it becomes shrivelled, but still retains its structural character 

 minus the wandering cells. It may be, therefore, that the canalicular 

 nuclei may be able to keep the cord in repair, as it were, by the matters 

 absorbed from the liquor amnii, until that fluid disappears, very much as 

 ivy continues to live after its connexion with the root has been severed. 

 Indeed the resemblance between the umbilical cord and vegetable tissue 

 is a very close one, as I have previously indicated, and as I may in future 

 communications be able to make still more clear. 



Appendix.- — Received June 14, 1875. 



Since the preceding note was written, I have been able completely 

 to verify Virchow's depiction of the arrangement of capillaries on the 

 surface of the cord, in continuity with those of the dermal ring. 



The existence of this arrangement, however, must be exceptional, and 



