912 OF GENERATION ACTION OF THE FEMALE. 



animals, as to secure a very close conformity to a common standard. 1 There 

 is evidence that the occurrence of the uterine nisus may be induced by a 

 variety of causes, several of which probably concur in the normal act of 

 Parturition. For, in the first place, the state of development of the muscu- 

 lar substance of the Uterus can scarcely be without a considerable influence 

 on this operation. We see it undergoing a gradual augmentation during the 

 period of pregnancy, without any demand being made upon its functional 

 activity; it gradually becomes more and more irritable, contractions being 

 far more readily excited in it by electrical or other stimulation, in the later 

 than in the earlier months of pregnancy; and at last this irritability seems 

 to reach its acme, in virtue of the nutritive changes which have been pro- 

 gressively taking place in it, and to discharge itself in one powerful effort. 

 Certain preparatory changes are known to be taking place in the Uterus 

 itself, during the last two or three weeks of gestation ; for its upper part 

 contracts more closely around its contents, as if it were bracing itself up for 

 the coming encounter; whilst there is a greater disposition to relaxation of 

 its lower part, as also in the soft parts surrounding the orifice of the pelvis, 

 so that the whole mass descends. It is well known that there is far less apti- 

 tude for dilatation in the os uteri before this change has taken place; so that 

 premature labors are frequently rendered very difficult and tedious by the 

 resistance which the foetus encounters from the soft parts, notwithstanding 

 that its smaller size enables it to pass more readily through the pelvic canal. 

 -That the parturient effort, however, is not solely dependent upon the state 

 of development of the uterus, appears from several considerations ; and, in 

 the first place, from the very curious fact that, in cases of extra-uterine 

 fo3tation, contractions resembling those of labor take place in its walls. In 

 fact, what may be termed the maturation not merely of the Uterus, but also 

 ofits Embryonic contents, a condition analogous to that which precedes 

 the dropping of ripe fruit, and which is acquired by the completion of the 

 developmental process, appears to have more influence in determining the 

 normal parturient effort, than any other cause which can be assigned. The 

 Placenta of the fully developed fetus, indeed, is somewhat in the condition 

 of the footstalk of a ripening fruit; that is, having attained its full evolution 

 as an organ of temporary function, its connection tends to become dissevered 

 in virtue of the further changes which take place in itself, quite irrespectively 

 of any external agency. 2 This is very strikingly evinced by the fact, that 

 when the uterus contains two foetuses, and one of them is expelled, either 

 in consequence of impeded development or disease in itself, or because it has 

 attained its own full term of development (as in cases of superfetation, 

 766), the other, if its development at this period is far from complete, is 

 often retained, and goes on to its full term, its placenta not being detached 

 in the first parturient effort, because it was not then prepared for the separa- 

 tion. It is obvious that this view affords a rational explanation of the oc- 

 currence of uterine action in cases of extra-uterine fetation ; for, if the con- 

 dition of the placental attachment furnish its exciting cause, it will do so 

 equally, whether the placenta be attached to the lining of the uterus, or to 



1 This may he best illustrated by the analogy of a Lcydon jar which is being 

 charged by the continuous action of an Electrical Machine, and which is so arranged 

 as to r//,scharge itself spontaneously whenever the disturbance in its equilibrium at- 

 tains a certain intensity. If the movement of the machine be uniform, and other 

 conditions remain the same, the discharge will take place at regular intervals. 



2 Such a change may be easily verified in the Placenta of many of the lower ani- 

 mals, Midi as the Cat, in which the fuetal and maternal portions remain more distinct 

 from each other than they do in the Human female ; for these become far more ea.-ily 

 separable as the period of parturition draws near than they are at any previous time. 



