262 DETERMINING CAUSES. 



ductus venosus, and foramen ovale, as they do not take place to the 

 same extent in every foetus, be the cause of a phenomenon whose 

 period very rarely varies, and with which variations it has besides 

 no correspondence. 



665. An anonymous author, who was for a long time opposed by 

 Millot, speaks of a vacuum that takes place in the sac of genera- 

 tion, in consequence of the transudation of its waters, and pretends 

 that the uterus, obeying its natural elasticity, closes up so as to re- 

 move this void; but it is easy to perceive that this author mistakes 

 the effect for the cause, and has misunderstood the question. 



666. Steinzel and others have referred the occasional cause of 

 parturition to the periodical nisits of each menstrual period. But 

 in the first place many pregnant women are met with, in whom the 

 habit of menstruation has never been exhibited. Now the influence 

 of habit is felt so much the more powerfully the nearer we are to the 

 itstant when it was left off. Yet, in the hypothesis of Stein, pre- 

 cisely the contrary is remarked. Besides, in order to see at once 

 the futility of such a theory, it is merely necessary to advert to the 

 fact, that the ninth catamenial revolution takes place in some 

 females at the commencement of the eighth month, in others at 

 the seventh, often at the end of the tenth, and that a good many wo- 

 men do not menstruate more than two or three times a year, while 

 the differences observed in the duration of pregnancies are so few, 

 that many persons still doubt as to their existence. 



667. MM. Lobstein and Chaussier seem to admit that this cause, 

 which has been so much sought for, is found in the completion of 

 the organisation of the womb, which waits until the muscular 

 character of its fibres is fully developed before it contracts. But 

 miscarriages and premature labors fully demonstrate the insuffici- 

 ency of such an explanation. 



668. According to Loder the extensibility of the womb is con- 

 fined within certain limits; the fibres of the womb fatigued by a 

 long continued state of distention, being unable to yield any further, 

 react, at the end of the ninth month, upon the body that had kept 

 them so long extended, and thus decide the act of parturition; but 

 upon reflecting that the development of the womb is not a passive 

 phenomenon, that twin pregnancies, or those where the ovum from 

 some cause attains to very great dimensions, do not terminate any 

 sooner than those where the womb acquires but a very small size, 

 we are compelled to reject this hypothesis also. 



669. The opinion of Levret and Baudelocque, entertained also 

 by M. Desormeaux, has at the present day the greatest number of 

 partisans. Founded on the arrangement of the uterine fibres, and 



