PARTURITION. 1003 



the neck of the uterus also becomes obliterated, and after ten periods of 

 ovulation, therefore about the two hundred and eightieth day of preg- 

 nancy, labor-pains set in for the expulsion of the contents. The pains are 

 separated by intervals of freedom; each pain, further, begins gradually, 

 then reaches its height, and diminishes slowly. With each pain the 

 temperature of the uterus increases. The activity of the fetal heart is, 

 further, somewhat slowed and enfeebled with each pain, as a result of 

 irritation of the vagus in the oblongata of the fetus. 



The uterine contraction passes in a peristaltic manner from the tubes to the os 

 in from twenty to thirty seconds. The curve traced by this movement has usually 

 a much more steep ascending than descending limb; rarely the reverse; occasion- 

 ally, both limbs are alike. The curve of contraction increases slowly, persists on 

 the average about eight seconds at its height, and then falls in from five to twenty- 

 five seconds. The frequency of the pains increases to the conclusion of labor. 

 The pains are shortest in the first half of the period of dilatation, while the ele- 

 vation of the curve is lowest, and the intervals are long; in the second half the 

 pains become longer and stronger with the dilatation of the os; and combined 

 pains appear (like superposed contractions). In the first half of the period of 

 expulsion the curves are higher, in the second half more frequent and higher, 

 but of shorter duration and with shorter intervals. 



The pressure within the uterine cavity during a maximal contraction increases 

 from i to 6 fold in the course of labor in consequence of the progressive expul- 

 sion. The increase in pressure depends upon the increased thickness of the uterine 

 walls, somewhat also upon their increased curvature. Both factors would of 

 themselves tend to increase the degree of pressure, were it not that the strength of 

 the muscular fibers is considerably reduced by the shortening that occurs in the 

 process of evacuation of the uterus. 



Polaillon estimates the pressure that the uterus exerts upon the ovum with 

 each pain at 154 kilos; and that the uterus with each pain performs work equal 

 to 8820 kilogram-meters. The intra-uterine pressure is greatest up to the rupture 

 of the membranes, after which it diminishes, to regain its maximum toward the 

 end of labor (on making bearing-down efforts it may reach 400 mm. of mercury). 



After expulsion of the fetus the placenta remains behind for a time, and about it, 

 with further pains, the uterus contracts tightly. In consequence a not inconsider- 

 able amount of placental blood flows to the child. Therefore, it may be advis- 

 able not to tie the umbilical cord immediately after the birth of the child. After 

 some time placenta, fetal membranes, and decidua are expelled as the after-birth. 



With respect to the dependence of the movements of the uterus upon the 

 nervous system, the following is known: (i) Irritation of the hypogastric plexus 

 causes contraction of the uterus. The fibers arise from the spinal cord (the last 

 dorsal and the 3d and 4th lumbar vertebrae), enter the abdominal sympathetic, 

 and pass from here into the plexus named. (2) Also irritation of the nervi 

 erigentes, arising from the sacral plexus, has a motor effect. (3) Irritation of 

 the lumbar and sacral portions of the spinal cord causes strong movements. 

 A center for the act of parturition is situated in the spinal cord. (4) The uterus 

 probably possesses, like the intestine, parenchymatous centers of its own, which 

 can be stimulated to movement by suspension of respiration and anemia (through 

 compression of the aorta or rapid hemorrhage). Reduction in the bodily tem- 

 perature diminishes, while increase augments the contractions, which cease in 

 the presence of high fever. The experiments made by Rein on pregnant bitches, 

 in which he divided all of the nerves passing to the uterus, have yielded the re- 

 markable result that, in the uterus freed from all connection with the cerebro- 

 spinal centers, all of the principal phenomena are possible that are connected 

 with impregnation, pregnancy, and parturition. The uterus must, therefore, 

 possess its own automatic ganglia, under whose control the processes named 

 take place. According to Dembo, a center is situated in the upper portion of 

 the anterior vaginal wall (rabbits). According to Jastreboff the vagina of the 

 rabbit undergoes independent rhythmical contractions. Sclerotic acid excites 

 the movements energetically, as does likewise anemia. (5) v. Basch and Hoffmann 

 observed reflex contractions after irritation of the sciatic; Schlesinger after cen- 

 tral irritation of the brachial plexus; Scanzoni after irritation of the nipples in 

 man. (6) The uterus contains for its vessels both vasoconstrictors (by way of 

 the hypogastric plexus), derived from the splanchnic, and vasodilators (by way 



