564 Diseases of the Gejiital Orga7is 



branes. In the early stages of pregnancy, however, the 

 chorionic tufts and placental crypts are so primitive that 

 recognizable incarceration does not occur because the pla- 

 cental disease quickly runs its course and placental separa- 

 tion occurs prior to fetal expulsion, so that the abort is ex- 

 pelled, enclosed within its membranes. As pregnancy ad- 

 vances, the increasingly complex placental structures invite 

 an equally increasing incarceration of the chorionic tufts, 

 until in the sixth or seventh month the expulsion of the 

 fetal cadaver usually reveals the presence of a severe pla- 

 centitis, as evidenced by the retention of the fetal mem- 

 branes. When a cow or heifer aborts, the probability of re- 

 tention of the fetal membranes increases as she approaches 

 full term and the intensity of the retention increases 

 along parallel lines. If the intra-uterine infection is ex- 

 tensive but fails to accomplish the death of the fetus and 

 its expulsion, there occurs at birth a retention of fetal 

 membranes often more severe and perilous than observed 

 after abortion. When abortion occurs at a late date, reten- 

 tion of the membranes after the expulsion of the fetal cada- 

 ver may not occur, because the placentitis has completed its 

 course up to the point of dehiscence of the chorionic pla- 

 centae. That is, there is no invariable rule of relationship 

 between the death of the fetus and its expulsion from the 

 uterus. They are two separate phenomena. The irritation 

 in the uterus due to the endometritis may excite uterine con- 

 tractions and cause the expulsion of the fetus while the 

 latter is yet alive (premature birth). Usually the death of 

 the fetus and its expulsion from the uterus occur almost 

 simultaneously, so that the fetal cadaver is fresh when ex- 

 pelled. But the fetal cadaver may be detained in the uterus 

 for an indefinite period for any one of not less than three 

 different reasons: (1) The expulsion of the embryo may be 

 delayed or prevented by cervicitis with sclerosis or adhesions 

 of the cervical tissues. (2) The uterus may be too paretic 

 to expel promptly the fetal cadaver. (3) The expulsion of 

 the cadaver may be inhibited by the presence in the uterus of 

 a second living fetus (twins) . The latter force is more nota- 



