PREGNANCY. PARTURITION. CHILDBED. 325 



as 100 mm Hg. By these contractions the foetus is pressed 

 against the cervical canal, which dilates and stretches so that 

 the uterus and the vagina form a common tube. The mem- 

 brane of the egg (the decidua reflexa of the utrinal mucous 

 membrane, the chorion and the amnion) are ruptured so 

 that the amniotic fluid is discharged. By further contraction 

 of the uterus the child is forced through the vagina and 

 pelvis, generally head-foremost. Parturition is aided by 

 compression of the abdomen. -Soon after the birth of the 

 child the placenta is loosened by the further contraction of 

 the walls of the uterus and, under loss of some blood, is 

 discharged with the egg membranes (after birth). 



The innervation of the uterus takes place by means of the 

 nerves from the lowest thoracic and from the lumbar cord. 

 A part of the fibres pass through the sympathetic, while 

 another part pass directly with the sacral nerves to the 

 uterus. The centre for the contraction of the uterus lies in 

 the lumbar cord. This centre can be stimulated reflexly by 

 stimulations from the centripetal nerves of the uterus. These 

 centripetal nerves are stimulated by the tension in the walls 

 of the uterus caused by the growing foetus. In dogs in 

 which the lumbar cord is separated from the rest of the 

 nervous system, normal parturition can still take place. 



The duration of parturition varies. In case of the first- 

 born it may last 20 hours, but in subsequent cases it is 

 shorter. During parturition the contractions of the uterus 

 gradually become more intense, frequent, and longer until 

 the child is expelled. These contractions are accompanied 

 by pain. During each "pain" the temperature, rate of 

 pulse, and perspiration are increased. 



After parturition the uterus assumes its normal form, 

 many of the muscle cells undergoing fatty degeneration. 

 The inner surface of the uterus acquires a new epithelial 

 lining, and after about four weeks the regeneration of the 

 mucous membrane is complete. As long as a mucous mem- 

 brane is not regenerated, it behaves like a wound and 

 secretes a corresponding wound secretion. This secretion 



