THE FEMALE SEXUAL ORGANS 699 



place., and this occasions a fall of the intrauterine pressure at the next pause. 

 After this fall, however, the pressure during the following pauses tends to 

 return to its original level, although that level is seldom reached, partly 

 because the amniotic fluid escapes during each contraction of the wall, and 

 partly because the child is pressed deeper and deeper into the pelvis, thus 

 decreasing the volume of the uterine contents. 



During a single pain the intrauterine pressure increases slowly at first, 

 then rather rapidly, and finally slowly again until it reaches its highest point. 



FIG. 303. Pressure curve of the last contraction of the uterus in parturition, after Westermark. 

 The high curve, reaching a pressure of 400 mm. Hg., represents the effect of the abdominal 

 muscles. To be read from left to right. 



For about eight seconds it remains at this maximum, after which it falls at 

 first slowly, then for five to twenty-five seconds more rapidly and at the last 

 very slowly (Fig. 302). 



The highest pressure due to the contractions of the uterus alone, attained 

 during the individual pains, increases during the progress of birth and reaches 

 its maximum at the end. Out of 587 determinations made by Westermark 

 the lowest was 20 mm. Hg., the highest 220, and the average 109 mm. The 

 value naturally is considerably increased when the abdominal pressure also is 

 brought to bear on the wall of the uterus. Especially is this the case during 

 the last pains of the expulsive period, where values of 400 mm. Hg. have 

 been observed (Fig. 303). 



A short time after the birth of the child the placenta becomes loosened and 

 with the amnion is expelled from the uterus as the afterbirth. The severe 

 hemorrhage which occurs at first is stopped by the powerful contractions of the 

 uterus. Then the organ gradually returns to its original size, the mucous mem- 

 brane becomes regenerated, the muscle fibers decrease in length and breadth. 

 Connected with these regeneration changes, which are complete after about two 

 months, there is for a couple of weeks a discharge of a slimy, and at first bloody, 

 material. The first menstruation however does not as a rule appear until about 

 the tenth month, when lactation has ceased (cf. 3). 



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