Normal Parturition 511 



inhibits expulsive muscular contractions of the uterus. We 

 have also learned, on page 165, that normally the corpus luteum 

 begins to disappear late during gestation and that at the time of 

 birth it has become completely atrophied. The relation of this 

 disappearance of the yellow body from the ovary to the expulsion 

 of the fetus has not been studied and may be quite interesting, 

 as it possibly exerts a highly important influence upon birth. 

 We know that the death of the fetus, as already stated, tends 

 constantly to excite a reflex action in the uterine walls, which 

 brings about contractions and the expulsion of the dead fetus. 

 We know also that, in case of the aseptic death of the fetus, 

 followed by mummification, the presence of the cadaver does not 

 excite this reflex action, but permits the dead fetus to remain as 

 an inert body in the uterine cavity for an indefinite period "of 

 time. It therefore seems that it is not so much the death of the 

 fetus which, in this case, causes its expulsion as it is a beginning 

 of putrefaction. It is not impossible that the excretions of the 

 fetus after a time become so important in quantity and character 

 that, passing into the blood of the mother, they bring about a 

 certain irritation upon the central nervous system and cause con- 

 tractions of the uterus, with the expulsion of its contents. 



The Expelling Powers. The initial powers by which the 

 fetus is expelled from the uterus reside in the unstriped muscle 

 walls of the uterus itself, but the final power is very largely de- 

 rived from the abdominal walls, including the diaphragm. 



I,abor pains are diminished or inhibited in many cases by cir- 

 cumstances of varying character. When there is torsion of the 

 uterus to an extreme degree, there are no prominent labor pains 

 present, because the contractile power of the uterus is destroyed. 

 In transverse development of the fetus in the uterus of the mare, 

 the physical relations of the fetus to the organ are such that they 

 inhibit any very marked labor pains, and while we have good 

 evidence of some uterine contraction, by the dilation of the os 

 uteri and the expulsion of portions of the fetal membranes, we 

 do not observe the vigorous expulsive efforts of normal parturi- 

 tion. It may be stated that we do not generally observe a full 

 exertion of the expelling powers in any of those cases wherein 

 the conditions are such that the fetus cannot pass from the uterus 

 through the cervix into the vagina. 



