854 PARTURITION. 



movements induced by stimulating these two tracts are somewhat different, 

 and moreover that the sympathetic tract is vaso-constrictor and the spinal 

 tract vaso-motor in nature ; but the matter has not yet been fully worked out. 



798. We are, however, hardly justified in considering the rhythmical 

 contractions of the uterus during parturition as simple reflex acts excited by 

 the presence of the foetus. We are utterly in the dark as to why the uterus, 

 after remaining apparently perfectly quiescent (or with contractions so slight 

 as to be with difficulty appreciated) for months, is suddenly thrown into 

 action, and within, it may be, a few hours or even less get rid of the burden 

 it has borne with such tolerance for so long a time ; none of the various 

 hypotheses which have been put forward can be considered as satisfactory. 

 And until we know what starts the active phase, we shall remain in ignor- 

 ance of the exact manner in which the activity is brought about. The 

 peculiar rhythmic character of the contractions, each " pain " beginning 

 feebly, rising to a maximum, then declining, and finally dying away alto- 

 gether, to be succeeded after a pause by a similar pain just like itself, pain 

 following pain like the tardy long-drawn beats of a slowly beating heart, 

 suggests that the cause of the rhythmic contraction is seated, like that of the 

 rhythmic beat of the heart, in the organ itself. And this view is supported 

 by the fact that contractions of the uterus similar to those of parturition 

 have been observed in animals even after complete destruction of the spinal 

 cord ; and the movements induced by asphyxia seem in part, and those 

 caused by some drugs such as ammonia seem to be wholly, due to an intrin- 

 sic action of the uterus itself. Nevertheless, general evidence supports the 

 conclusion that, in a normal state of things at all events, the contractions of 

 the uterus, like those of the lymph-hearts, are largely dependent on the 

 spinal cord. 



The occurrence of contractions in conseqence of an asphyxiated condition 

 of the blood explains why, when pregnant animals are asphyxiated, an ex- 

 trusion of the foetus frequently takes place. There is no evidence, however, 

 that the onset of labor is caused by a gradual diminution of oxygen in the 

 blood, reaching at last to a climax. Nor are there sufficient facts to connect 

 parturition with any condition of the ovary resembling that of menstruation. 



The action of the abdominal muscles in parturition is, on the other hand, 

 obviously a reflex act carried out by means of the spinal cord, the necessary 

 stimulus being supplied by the pressure of the foetus in the vagina or by the 

 contraction of the uterus. Hence the whole act of parturition may with 

 reason be considered as a reflex one. 



Whether it be wholly a reflex or partly an automatic one, the act can 

 readily be inhibited by the action of the central nervous system. Thus 

 emotions are a very frequent cause of the progress of parturition being sud- 

 denly stopped ; as is well known, the entrance into the bedroom of a stranger 

 often causes for a time the sudden and absolute cessation of "labor" pains, 

 which previously may have been even violent. Judging from the analogy 

 of micturition, between which and parturition there are many points of 

 resemblance, we may suppose that this inhibition of uterine contractions is 

 brought about by an inhibition of the centre in the lumbar cord. 



799. After the expulsion of the foetus, the foetal placenta separates 

 from the uterine walls, and is, together with the remnants of the membranes, 

 expelled after it. The uterus then falls into a firm tonic contraction similar 

 to that of the emptied bladder, by which means hemorrhage from the vessels 

 torn by the separation of the placenta is avoided. The lining membrane of 

 the uterus is gradually restored, the muscular elements are reduced by a 

 rapid fatty degeneration- and in a short time the whole organ has returned 

 to its normal condition. 



