CHAP, ii.] PREGNANCY AND BIRTH. 399 



fibres undergoing fatty degeneration, and thus the mucous and 

 muscular walls are gradually brought back to their natural con- 

 dition. During the early days of this process of involution a 

 discharge, the lochia, takes place from the internal surface of the 

 uterus. 



967. The whole process of parturition may be broadly con- 

 sidered 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 administration 

 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 spontaneous 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 stimu- 

 lation of the spinal cord at any part of its whole length as well 

 as of various regions of the brain ; the analogy with the move- 

 ments 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 

 asphyxiated ; 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 er- 

 got which increase uterine contractions probably in like manner 

 produce their effect chiefly at least through their action on the 

 nervous centre. The ready way in which the uterus enlarged by 

 pregnancy responds by reflex contraction to the stimulation of 

 various afferent nerves is illustrated in the human subject by the 

 means usually adopted to secure after the birth of the child that 

 continued contraction by which haemorrhage is avoided. Should 

 for any reason such a contraction fail to take place, it may be 

 secured by applying cold or pressure to the abdominal walls or 

 by introducing a hand or some foreign body into the vagina, or, 

 what perhaps best illustrates the reflex nature of the matter, by 



