CHAP, ii.] PREGNANCY AND BIRTH. 1127 



In the roof of the uterus, in the region of the placenta, the 

 amniotic fluid is in close proximity not only to the branching 

 umbilical arteries and veins of the fcetus, but also to many 

 of the maternal blood vessels, being separated from the maternal 

 blood by nothing more than the thin wall of the blood vessel 

 and the membrane just spoken of. The fluid is also over the 

 rest of the internal surface of the uterus, in close proximity to 

 the blood vessels of the maternal decidua, and indeed in the 

 later stages, when the decidua apart from the placenta has 

 largely retrograded, to the blood vessels of the uterine mucous 

 membrane. The conditions therefore are favourable for the 

 transudation of material from the blood of the mother into the 

 amniotic cavity ; and we have experimental evidence that not 

 only water but various substances may pass in this way from 

 the one to the other. If indigo-carmine ( 336) be injected 

 into the veins of the mother, none passes by the umbilical vein 

 into the tissues of the fcetus ; these remain wholly uncoloured. 

 Yet the amniotic fluid becomes deeply tinged with the pigment, 

 which obviously must have passed directly from the mother 

 into the amniotic cavity. Hence we may conclude that though 

 the amniotic fluid is at first derived exclusively from the 

 fcetus, and during the whole time is partly derived from the 

 same source, it is also, and especially in the later stages, largely 

 derived by direct transudation from the mother. 



Into this amniotic space the passages of the foetus, the 

 mouth, anus, &c. open, and it serves as we shall see as a reposi- 

 tory for the excretions of the fcetus. Into it is discharged 

 such urine as the fcetus secretes, into it are shed, the foetal 

 epidermic scales, and appendages such as hairs, and into it may 

 be discharged the contents of the alimentary canal, known 

 as the meconium. Now, hairs, epidermic scales, in the case 

 of hoofed mammals portions of shed hoofs, and at times 

 meconium have been found in the foetal stomach; they arrived 

 there by the fcetus swallowing the amuiotic fluid; we have 

 other evidence that the fcetus in the uterus may execute 

 swallowing movements, and if these are executed they must 

 lead to swallowing of the amniotic fluid, since this will pass 

 into the mouth and pharynx whenever the mouth is opened. If 

 these swallowing movements occur frequently, and there is 

 some evidence that they do, nutritive material contained in the 

 fluid and derived directly from the mother, mi^ht thus be con- 

 veyed to the f(Btus; the latter mi-jlit l>e nourished by means of 

 the amniotic fluid. But, even making all allowance for any 

 possible nourishment in this way, we may probably regard it as 

 insignificant compared with that which is carried on by the 

 placenta! and umbilical vessels; we may assume that the food 

 of the fcetus reaches it mainly l>y pas^iii^ from the maternal 

 sinuses into the capillaries of the chorionic villi. 



