722 



UTERUS AND ITS APPENDAGES. 



the placenta, the blood of the mother is 

 brought into mediate relation with that of 

 the foetus. Two currents, the one foetal, and 

 the other maternal, are continually flowing 

 into and from this organ, yet in channels so 

 perfectly distinct that no direct commingling 

 of the streams can ever take place. Never- 

 theless, though no passage of the form-ele- 

 ments of the blood can occur, yet through 

 the partition- walls which separate these two 

 currents, all the materials necessary to the 

 growth of the foetus are conveyed by endos- 

 motic processes, and all the changes necessary 

 to the respiration of the foetus, and to the 

 elimination of effete materials, are effected. 

 The mechanism by which these ends are 

 accomplished is of two kinds. The one 

 consisting of means for bringing the two con- 

 stantly flowing streams of blood into juxta- 

 position, the other of instruments forearming 

 on the nutritive and eliminative processes 

 which are the objects of this conjunction. 



The foetal blood conveyed by the branches 

 of the two umbilical arteries, is distributed to 

 the villi, whence, after being exposed, in the 

 finer vessels and capillaries which ramify upon 

 their inner surface, to the influence of the 

 maternal blood, it is returned to the funis by 

 the branches which terminate in the single 

 vein. The propelling power by which the 

 blood is moved resides in the heart of the 

 foetus, and the whole of its circulating fluid is 

 thus carried in successive portions through 

 the placenta. 



The maternal blood, after having its im- 

 petus diminished by the spiral course which 

 the arteries take in passing through the walls 

 of the uterus, as well as through the decidua, 

 is delivered at once into the placenta, where 

 it becomes immediately separated into fine 

 streamlets by the villi which are so closely 

 set as to break up the interior of the organ 

 into countless channels. After flowing every- 

 where among the villi, the blood escapes back 

 into the uterine system * by the venous ori- 



* I can arrive at no other conclusion than that 

 the blood in the interior of the placenta, is as much 

 external to the maternal vascular system as it is 

 while passing through a quill inserted between the 

 divided ends of a vein in a living animal. Although, 

 in this belief, I find myself opposed to the views of 

 Weber, Miiller, J. Reid, Goodsir, and Schrceder van 

 der Kolk, who, with certain differences maintain 

 that the blood is still retained within the maternal 

 system. The views of these and of many other 

 pli3'siologists, who more or less agree with them, 

 are divisible into two classes. According to one 

 view, the uterine vessels either form a network in 

 the substance of the placenta (Weber), or become 

 expanded into an enormous sac, composed of the 

 inner coat of these vessels, which envelopes every- 

 where the surface of the villi (J. lieid), so that the 

 blood after circulating within the placenta is re- 

 turned to the uterus without having been extrava- 

 sated. According to the other view (Goodsir and 

 Schrceder van der Kolk), the decidua throws a close 

 investment over every villus, and forms that outer 

 covering of cells which I have ascribed to the 

 chorion ; so that in this view a lamina of uterine 

 structure still separates the maternal blood from the 

 exterior of the villi. 



On this and other points relating to the minute 



fices upon the surface of the decidua, and 

 upon the dissepiments and marginal furrows 

 from which it is conducted, through the deci- 

 dual coat, to the sinuses in the substance of 

 the uterus, and thence is returned to the 

 mother's body by the uterine and spermatic 

 veins. 



During the flow of these streams throush 

 the interior of the placenta, the surface of the 

 villi is constantly bathed by the maternal 

 blood. Nevertheless the blood of the foetus 

 is separated from that of the mother first, 

 by the walls of its own capillaries ; secondly, 

 by the gelatinous membrane in which these 

 ramify ; and thirdly, by the external non-vas- 

 cular nucleated sheath derived from the cho- 

 rion. With the latter alone, the maternal 

 blood is brought into direct contact. 



Each of these structures has its distinct 

 office. The use of the external layer of cells 

 {fig. 485. b) has been happily illustrated by 

 Uoodsir. They are to the ovum what the 

 spongioles are to the plant : they supply it 

 with nourishment from the soil in which it is 

 planted. Thus their action is selective, and 

 they transmit to the interior of the villus the 

 materials necessary for foetal growth. These 

 again are taken up by the internal layer of cells 

 {Jig. 485. b), and by them brought into direct 

 contact with the fcetal capillaries. By a similar 

 process, the interchanges necessary to respira- 

 tion are effected through the membranous sur- 

 faces which separate the maternal and fcetal 

 blood. And these processes, respiratory and 

 nutritive, are continued without intermission 

 from the moment that the two separate cur- 

 rents are established until the final separation 

 of the foetus in the act of birth. Yet, through- 

 out pregnancy, the form of the mechanism by 

 which these changes are effected is continually 

 altering, either in its greater or lesser parts. 

 The greater changes have reference chiefly to 

 mechanical, and the lesser to vital necessities. 

 The changes in form exhibit a beautiful series 

 of adaptations in the capacity and strength of 

 the placenta to the increasing amount and 

 force of the maternal current. The original 

 plan of the placenta, that of an interspace be- 

 tween two spheres (a lesser one contained 

 within a greater) filled by maternal blood, 

 could not be long preserved with the materials 

 out of which the temporary organ is con- 

 structed. For as the ovum grows, the deci- 

 dua reflexa, which alone confines the blood 



structure and composition of the placenta, consult 

 Von Baer, Untersuchungen liber die Gefttssver- 

 bindung zwischen Mutter und Frucht in den Sati- 

 gethieren. 1828. Ritgen, Beitrttge zur Aufhellung 

 der Verbindung der Menschlichen Frucht mit dem 

 Frucbthftlter. 1835. Sharpey, in JMliller's Physi- 

 ology by Baly. 1887 and 1848. Eschricht, Do orga- 

 nis qua; respiration! et nutrition! foetus mammalinm 

 inserviunt. 1837. E. H Weber, in Hildebrandt's 

 Anatomic, b. iv., and in Wayner, Elements of Phy- 

 siology. 1841. J Reid, E'dinb. Med. and Surg. 

 Journ., No. 146. J. Dalrymple, Medico-Chifurgical 

 Trans., vol. xxv. 1842. Goodsir. J. and //., Anatom. 

 and Pathol. Observs. 1845. Scliroeder van der Kolk, 

 Waarnemingen over het Maaksel van de Mensche- 

 lijke Placenta, en over haren Bloods-omloop. 1851. 



