BAG OF WATERS. 283 



really took place, the surface of the bag would become" covered Avith 

 small drops of water, or a kind of dew, in a word, it would become 

 moist, during the pains, whereas, it is never drier than it is during the 

 very strongest contractions; besides, it has already been seen that 

 there is no analogy between the liquor amnii and the glairy dis- 

 charges, into the composition of which A. Petit gratuitously sup- 

 posed them to enter so readily. 



710. The bag of waters, like the dilatation of the cervix, is pro- 

 duced by the contractions of the womb, and by a mechanism equally 

 easy to be understood: by acting upon the periphery of the ovum as 

 upon the throat of a pulley, the uterine fibres compel it to descend, 

 while, on the other hand, the cervix, by dilating, is obliged to ap- 

 proach nearer to the fundus, and to leave a more or less considerable 

 segment of the membranes outside of the orifice; the point of the 

 foetal ovoid, lubricated with mucus, forces the orifice to open a little, 

 as the finger, when previously covered with a peach skin turned in- 

 side out, will force the fingers of the other hand to open when we 

 try to push it betwixt them. It would, notwithstanding, be wrong 

 absolutely to deny the extensibility of the tunics of the foetus. On 

 the contrary, every thing proves that they may sometimes extend to 

 a considerable degree, and that it is in consequence of this elonga- 

 tion that the bag in certain cases aflects the form of a cone or of a 

 pear; I merely wish to say that this property is in general very slight. 

 Even if it be true that the amniotic lymbal is almost always curved 

 upon a cord that is shorter than the rest of the ovum, it is also true 

 that this peculiarity, which seems to demonstrate that the membranes, 

 have yielded at that point, is owing to another cause; any one who 

 has had occasion carefully to open a pregnant womb, has had an 

 opportunity of being convinced that the mere weight of the ovum is 

 sufficient to flatten it very considerably, as soon as it ceases to be 

 exactly supported by the surrounding organs: therefore, it is quite 

 evident that a portion of the membranes may in this state of relaxa- 

 tion engage very well in the os uteri, and in a very small volume, 

 without undergoing any real elongation. 



711. After having wholly, or in part, dilated the os uteri, the baw 

 of waters, now become very large, and besides, ill-supported in the 

 upper part of the vagina, yields to the impulsion of the liquid, and 

 breaks; the contained fluid escapes, and the head of the child beino- 

 at the same moment pushed forwards by the same effort, stops up 

 the passage to the rest of the liquor amnii. But this rupture is far 

 from always taking place at the same point, or under the same de- 

 gree of dilatation, or at the same stage of labor in all women. The 

 membranes may be too dense, too thick and too resisting, or too 



