REPRODUCTION. 919 



the human female the vaginal muscles do not appear to engage in the expel- 

 ling act, the uterine and the abdominal muscles alone sufficing and finally 

 forcing the child wholly outside the mother's body. In this gradual manner, 

 painful and dangerous alike to mother and child, the maternal organism forces 

 the offspring to forsake its sheltering and nutritive walls and begin its inde- 

 pendent existence. 



Third Stage of Labor. During the later expulsive contractions of the 

 second stage the placenta, being greatly folded by the diminution in the uterine 

 surface of attachment, is loosened from the uterine wall by a rupture taking 

 place through the loose tissue in the region of the blood-sinuses. The child, 

 when born, is joined to the loosened placenta by the umbilical cord, until the 

 latter is tied and cut by the obstetrician. The muscular contractions, now 

 almost painless, continue through the third stage, and the placenta is torn 

 from its attachment, everted, and carried gradually outward. The lining 

 membrane of the uterus from the placenta outward and for a considerable 

 depth is gradually torn free from the deeper parts through the spongy layer, 

 and with the attached chorion and amnion follows the placenta. As a rule, 

 this after-birth appears at the vulva within fifteen minutes after the expulsion 

 of the child ; it consists of the placenta, the amnion, the chorion, the detidua 

 reflexa, and a considerable portion of the detidua vera. 



Previous to the third stage slight bleeding from laceration of the passages 

 occurs. But with the loosening of the placenta and the accompanying rupture 

 of the placental vessels the maternal blood flows freely and continues to flow 

 from the uterine wall, chiefly from the placental area, until the after-birth is 

 discharged. The average loss of blood amounts to about 400 grams. At the 

 close of the third stage of labor the uterine contractions have so far proceeded 

 that the organ is compressed into a hard compact mass, the ruptured vessels 

 are contorted and compressed, and the bleeding is thereby largely stopped. 

 For several hours, however, slight hemorrhage continues as an accompaniment 

 to the post-partum contractions, but finally this ceases with the formation of a 

 blood-clot over the wounded surface. 



The third stage of labor may continue through one or two hours. It is 

 customary, however, for the obstetrician speedily to put an end to it by assist- 

 ing the removal of the after-birth. 



Nature of Labor. Our knowledge of the nature of the muscular phe- 

 nomena of labor is incomplete. The uterine contractions are in part automatic 

 and in part reflex, but to what extent the former, and to what the latter, is not 

 known. Nerves reach the uterus partly through the abdominal sympathetic 

 chain and partly directly from the spinal cord through the sacral plexus. 

 Rein 1 found that in the rabbit after section of all uterine nerves normal 

 conception, pregnancy, and birth may occur. In some animals uterine move- 

 ments may continue after removal of the organ from the body. Such and 

 other observations indicate the existence of an automatic contractile power 

 resident in the organ itself. Since nerve-cells are not found in its walls, it 

 1 G. Eein : Pflugeifs Archiv fur die gesammte Physiologic, xxiii., 1880. 



