1140 PARTURITION. [Book iv. 



probably it is on account of its great usefulness that this peculiar 

 form of muscular activity is so prominent in the uterus. 



Even before labour proliferation of the epithelioid cells may 

 be observed in the lining membrane of the uterine vessels; these 

 arc rapidly increased after labour is completed, and form part of 

 the healing processes which follow. The tonic contraction of 

 which we have been speaking is maintained until the blood 

 vessels are permanently closed by these nutritive healing 

 processes. After birth the muscular elements of the uterus 

 dwindle, many of the fibres undergoing fatty degeneration, and 

 thus the mucous and muscular walls are gradually brought 

 back to their natural condition. During the early days of this 

 process of involution a discharge, the lochia, takes place from 

 the internal surface of the uterus. 



§ 708. The whole process of parturition may be broadly 

 considered as a reflex act, the nervous centre of which is placed 

 in the lumbar cord. In a dog, whose thoracic cord had been 

 completely severed, parturition took place as usual ; and the fact 

 that, in the human subject, labour will progress in a natural 

 manner while the patient is unconscious from the administra- 

 tion of chloroform, though it is often retarded and sometimes 

 arrested, shews that in woman also the contractions both of the 

 uterus and of the abdominal muscles are involuntary, however 

 much the latter may be assisted by direct volitional efforts. 



Observations on animals shew that even in a virgin uterus 

 and in one which is not enlarged by pregnancy movements can 

 be excited in a reflex manner through the central nervous 

 system and may occur rhythmically in an apparently sponta- 

 neous manner ; but the latter are often absent or are so slight 

 as readily to escape observation, and the former are often feeble 

 and excited with difficulty- In a pregnant animal on the other 

 hand, especially if pregnancy be advanced, powerful rhythmic 

 expulsive movements repeatedly occur in the apparent absence 

 of all extrinsic stimuli and are very readily provoked by the 

 stimulation of various afferent nerves. They may also be 

 induced by direct stimulation of the spinal cord at any part 

 of its whole length as well as of various regions of the brain ; 

 the analogy with the movements of the urinary bladder leads 

 us to suppose that the impulses thus started in the brain 

 and upper part of the spinal cord do not pass directly to the 

 uterus but throw into activity the reflex centre in the spinal 

 cord. Movements of the uterus are readily excited when the 

 blood ceases to be duly arterialized, extrusion of the foetus 

 being a common result when a pregnant animal is asphyxi- 

 ated ; and though the venous blood may act in part as a direct 

 stimulus to the uterine muscles the contractions are mainly due 

 to the blood exciting the nervous centre. Drugs such as ergot 

 which increase uterine contractions probably in like manner 



