CHAP, ii.] PREGNANCY AND BIRTH. 1139 



the beginning of which is the cause of the " show " spoken of 

 above, and which is considered to be a mechanical effect of the 

 uterine contractions hut which must be prepared for by 1 

 logical changes, during the early stages of labour extends up- 

 wards for two or three inches only; but, at the last, it is carried 

 right through the "decidual layer" of the placenta. Hence, 

 after the expulsion of the foetus, the uterus contains within its 

 cavity, separated from and now foreign to itself, the pl.t 

 and membranes, the latter consisting of amnion, chorion, the 

 whole of the remains of the decidua reflexa and a variable part 

 of the decidua vera; and, under normal conditions, these are 

 by the last expulsive efforts ejected with or immediately after 

 or soon after the child. As a rule the membranes are ruptured 

 and the amniotic fluid escapes before the head extrudes, but at 

 times the child is born still surrounded by the intact mem- 

 branes with their contained fluid; it comes into the world in 

 its "caul." 



When the placenta and membranes have left the uterus 

 (they not unfrequently are lodged for a while in the vagina), 

 the tonic contraction or "retraction" spoken of above, which 

 during the whole of labour has been following up the advance 

 of the foetus, and progressively lessening the uterine cavity, 

 continues is work and serves an important purpose. When the 

 last pain of labour, by which the emptied uterus is gathered up 

 into a small hard ball, passes away, the walls under normal 

 conditions do not wholly relax, a permanent tonic contraction 

 keeps the walls thick and in contact, thus closing the uterine 

 cavity; and over this compact and closed uterus waves of 

 rhythmical contraction, the " after-pains," still for a while pass 

 without altering its permanent condition. liy this continued 

 contraction or retraction, not only the open, torn ends of the 

 vessels of the decidua but all the vessels throughout the thick- 

 ness of the uterine walls are so compressed that all extensive 

 bleeding is prevented. Should this continued contraction 

 away to relaxation, haemorrhage or "flooding" follows. '1 his 

 retraction or tonic contraction, whatever be its exact nature, 

 which is so conspicuous in the uterus but which perhaps may he 

 recognized in a lesser degree as mere ordinary tonic contraction 

 in other rhythmically contracting organs, in the bladder, in the 

 intestine, and even in the heart, appears to serve more than one 

 purpose in the work of the uterus: by continually lessening the 

 uterine cavity it renders more efficient during labour the rhyth- 

 mic uterine " pains," by compressing the blood vessels during 

 labour it gradually shuts off the extravagant blood supply now 

 no longer needed, and by continuing that compression after 

 labour and by closing the uterine cavity it prevents hemorrhage 

 and wards off the evil effects which the tree entrance into tne 

 uterine cavity of foreign organisms might bring about. And 



