THE FEMALE GENERATIVE ORGANS 541 



attempts to reduce itself to its former size, and so expels its 

 contents. This idea receives some support from the fact that 

 twin pregnancies and hydramnios (or the presence of an 

 excessive quantity of hquor amnii) often result in premature 

 labour. 



(3) It has been supposed from early times onwards that 

 parturition might be brought about through the pressure of the 

 foetus producing a gradual dilatation of the cervix. WiUiams, 

 however, has pointed out that this condition of the cervix 

 cannot be the sole factor, since in a certain number of cases, 

 especially in twin pregnancies, a pronounced dilatation has 

 been known to occur for a considerable period prior to the 

 onset of labour. 



(4) Keilmann,'^ working upon the bat, came to the conclusion 

 that the onset of labour was caused by the increasing pressure 

 set up by the lower distended portion of the pregnant uterus 

 (the lower uterine segment) upon the surrounding nerve gangha. 

 Supposing this conclusion to be correct as a.ppUed to the bat, it 

 is not quite clear that it is equally apphcable to the human 

 female and to other animals. 



(5) Simpson ^ and others were of opinion that the " pains " 

 of labour were the indirect result of a partial separation of 

 foetus and decidua, brought about by the fatty degeneration of 

 the latter in the last stages of pregnancy, so that the foetus 

 became virtually converted into a foreign body, which caused 

 the uterus to respond accordingly. It is no doubt true that 

 part of the maternal placenta undergoes degenerative changes 

 towards the end of pregnancy, but there is no evidence that 

 this by itself is sufficient to cause a separation of the foetus from 

 the uterine waU. 



(6) There is no evidence in support of the theory that the 

 exciting cause of parturition is an accumulation of carbon 

 dioxide in the blood, beyond the fact demonstrated by Brown- 

 Sequard,* Keiffer,* and others, that uterine contractions can be 

 induced experimentally by this means. 



1 Keilmaun, " Znr Klarung der Cervixfrage,'' Zeitschr. f. Oeb. u. Oynak., 

 vol. xxii., 1891. ^ Simpson, loc. cit. 



' Brown-S^quard, Experimental Researches, English translation, London, 

 1853. * Keiffer, loc. cit. 



