CHAP, iv.] PARTURITION. 683 



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 intrinsic action of the uterus itself. Neverthe- 

 less 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 consequence of an asphyxiated 

 condition of the blood, explains why when pregnant animals are 

 asphyxiated, an extrusion of the foetus frequently takes place. There 

 is no evidence however that the onset of labour 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 contractions 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 suddenly stopped; as is well known, the 

 entrance into the bedroom of a stranger often causes for a time the 

 sudden and absolute cessation of 'labour' pains, which previously 

 may have been even violent. Judging from the analogy of mictu- 

 rition, between which and parturition there are many points of 

 resemblance, we may suppose that this inhibition of uterine con- 

 tractions is brought about by an inhibition of the centre in the 

 lumbar cord. 



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 haemorrhage 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 de- 

 generation, and in a short time the whole organ has returned to its 

 normal condition. 



