Pregnancy , or Gestation. 373 



These contractions are important for the development of the 

 power in the uterine walls which finally assumes a very necessary 

 function at the time of parturition, because it is largely 

 through these that the os uteri is dilated and the fetus is ex- 

 pelled. It is notable that it is in the multipara, where the uterus 

 is long and tubular, that the uterine contra;ctions play the great- 

 est part in the expulsion of the fetuses, while, in the unipara, 

 like the mare and cow, the principal expulsive powers at the 

 time of parturition reside in the abdominal walls and the uterus 

 performs a less conspicuous part in the act of birth. 



After the expulsion of the young from the uterus, it is again 

 liighly important that there should be a vigorous contractile 

 power in the organ, in order that it may expel, at an early period, 

 the fetal membranes and such portions of the uterine epithelium 

 as are cast off. It is needf'ft that the walls should contract 

 vigorously in order to check the amount of blood passing to the 

 organ and to close all capillaries in the uterine mucosa which 

 "have been opened during the process of separation between the 

 fetal membranes and the uterus. It is also important that the 

 uterine cavity shall be promptly closed and the epithelium of 

 its walls brought in contact. This contraction, too, indirectly 

 exerts a disinfecting, or bactericidial, power and serves to prevent 

 the entrance of infection or overcome any infection which may 

 have gained entrance into the cavity during or immediately after 

 the expulsion of the fetus. 



