NORMAL PARTURITION. 



Normal parturition is the birth or expulsion of the living fetus 

 at the natural time, without artificial assistance and in a state of 

 development which enables it to live. Although the act of 

 parturition is a physiologic one, it is accompanied by pain and 

 severe exertion upon the part of the mother and brings about 

 sudden changes in the life of both mother and fetus which in a 

 measure imperil the well-being of each. 



The phenomena of birth vary greatly in detail in species and 

 individuals and in no two are they precisely the same, either in 

 the period at which they occur after impregnation, the length 

 of time required for the expulsion of the fetus by the mother, 

 the amount of force required for its expulsion, or in any other of 

 the numerous details of this act. The fetus may present in many 

 different ways for its passage through the birth canal, or offer a 

 very wide degree of variations in detail and yet be virtually 

 normal. A very slight divergence in a given direction may cause 

 deviation of a part which may render birth more or less difficult, 

 or evenlmpossible without aid. 



The causes of parturition are not definitely known. We have 

 learned in preceding chapters that birth normally takes place 

 after a somewhat definite duration of intra-uterine life, but the 

 variations of the length of time in the larger animals, like the 

 mare and cow, may reach extremes of 90 days or more, so that we 

 cannot say that parturition is inevitable at a certain tirhe. We 

 know that the uterus and other portions of the genital tube un- 

 dergo certain developments during pregnancy which constantly 

 tend to fit them more and more for the act of birth, when that 

 phenomenon finally appears, but there seems to be nothing in 

 this development which marks a limit and designates a definite 

 stage at which the uterus will necessarily expel its contents. 



In studying the development of the fetus, we have noted that 

 certain changes take place in its organs of circulation and nutri- 

 tion and that they gradually acquire a completeness which closely 

 simulates that which is seen in the adult animal. In this way 

 the organism becomes fitted for an independent existence. 

 However, there is nothing in this development which seems to 

 mark a definite stage at which the fetus must be expelled. 

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