INVOLUTION OF THE UTERUS MECONIUM. 943 



contents of the uterus gradually lose their anatomical connection with the mother. When 

 tliis change has progressed to a certain extent, the uterus hegins to contract; each con- 

 traction then separates the membranes more and more, the most dependent part pressing 

 upon the os internum ; and the subsequent contractions are probably due to reflex action. 

 The first " pain " is induced by the presence of the foetus and its membranes as a foreign 

 body, a mechanism similar to that which obtains when premature labor has been brought 

 on by separation of the membranes. 



We shall not describe the mechanism of parturition, although this is entirely a physi- 

 ological process, for the reason that it is necessarily considered elaborately in works upon 

 obstetrics. The first contractions of the uterus, by pressing the bag of waters against 

 the os internum, gradually dilate the cervix ; the membranes usually rupture when the os 

 is pretty fully dilated, and the amniotic fluid is discharged ; the head then presses upon the 

 outlet; and, the uterine contractions becoming more and more vigorous and efficient, the 

 child is brought into the world, this being followed by the expulsion of the membranes and 

 placenta. There then follows a tonic contraction of the muscular walls of the uterus, 

 which becomes a hard, globular mass, easily felt through the flaccid abdominal walls. 

 The very contractions of the muscular fibres of the uterus which expel the foetus close 

 the vessels ruptured by the separation of the placenta and arrest the haemorrhage from 

 the mother. The changes which then take place in the respiration and the circulation 

 of the infant have been fully considered in connection with the development of the circu- 

 latory system. 



Involution of the Uterus. At from four to six days, and seldom later than eight days 

 after parturition, the uterus has sensibly advanced in the process of involution ; and it is 

 then gradually reduced to the size and structure which it presents during the non-preg- 

 nant condition, though it never becomes quite as small as in the virgin state. The new 

 mucous membrane, which has been developing during the latest periods of pregnancy, 

 becomes perfect at about the end of the second month after delivery. It has then united, 

 at the os internum, with the mucous membrane of the neck, which does not participate 

 in the formation of the decidua. The muscular fibres, after parturition, present granules 

 and globules of fat in their substance, and are gradually reduced in size, as the uterus 

 becomes smaller. Their involution is complete at about the end of the second month. 

 During the first month, and particularly within the first two weeks after delivery, there 

 is a sero-sanguinolent discharge from the uterus, which is due to disintegration of the 

 blood and of the remains of the membranes in its cavity, this debris being mixed with a 

 certain amount of sero-mucous secretion. This discharge constitutes the lochia, which 

 are at first red, but become paler as they are reduced in quantity and disappear. 



During lactation, the processes of ovulation and menstruation are usully arrested, 

 though this is not always the case. In treating of secretion, we have given a full descrip- 

 tion of the vernix caseosa, and we have also stated what is known with regard to the 

 properties and composition of the urine of the foetus. 



Meconium. M about the fifth month, there appears a certain amount of secretion in 

 the intestinal canal, which becomes more abundant, particularly in the large intestine, as 

 development advances. This is rather light-colored or grayish in the upper portion of 

 the small intestine, becoming yellowish in the lower portion, and is of a dark-greenish 

 color in the colon. The dark, pasty, adhesive matter, which is discharged from the rec- 

 tum soon after birth, is called the meconium. 



The meconium appears to consist of a thick, mucous secretion, with numerous grayish 

 granules, a few fatty granules, intestinal epithelium, and, frequently, crystals of choleste- 

 rine. The color seems to be due to granulations of the coloring matter of the bile, but 

 the biliary salts cannot be detected in the meconium by Pettenkofer's test. The con- 

 stituent of the meconium which, in our own observations, we have found to possess the 



