Expulsion of Fetal Membranes ; Invohition of the Uterus 529 



uterine walls invites infection. A contractile organ has in itself 

 the power to overcome infection ; hence the importance of the 

 normal contraction of the organ. Retention of the placenta will 

 be more fully considered later. 



The expulsion of the fetus and its fluids is at once followed by 

 contraction of the uterine walls, decreased vascularity, reduction 

 in size and obliteration of its cavity bj- the walls coming in con- 

 tact with each other. The placentae disappear, the glandular 

 layers of the deciduate placentae are detached and removed and 

 anew epithelial layer formed at the site of placental attachments. 



The cervix uteri contracts rapidly and the cervical canal is 

 well closed in 24 to 48 hours. The uterus, once pregnant, fails 

 to wholly regain the size of the virgin organ. The broad liga- 

 ments retract and again suspend the uterus. 



Collectivel}' we know these processes as involution of the 

 uterus, and regard them as highly important to the well-being of 

 the animal. When the uterus contracts in a physiologic manner 

 it tends to prevent infection of its walls, but if there is inertia or 

 paralj^sis of the walls, infection is probable. If afterbirth or 

 other dead tissue remains in the uterus and becomes infected, 

 the infection not only brings about an inflammation of the 

 uterine walls, but also increases the inertia or paralysis of them. 



In most domestic animals, the mother habitually devours the 

 entire fetal membranes immediately after their normal expulsion. 

 This regularly occurs in ruminants and the sow, and some- 

 times, it is said, in the mare also. It has been suggested 

 that the devouring of the fetal envelopes by the mother is the 

 persistence of a precautionary measure from the wild state, for 

 the defense of the mother and new-born against predatory 

 animals, by destroying the evidences of the recent birth. The 

 devouring of the membranes rarely results in accident, but there 

 have been a few ca.ses recorded where a cow has become choked 

 upon her placenta and, in one case personally related to us, the 

 cow became choked while the one end of the placenta still re- 

 mained firmly attached in her uterus. Sometimes the placenta 

 decomposes in the rumen or other portions of the alimentary 

 canal and causes indigestion. 



34 



