68 OF VITAL MOTION. 



react upon the uterus, and cause further contraction, 

 further constriction of the placental vessels, and further 

 depression of the life of the foetus, and this latter 

 change, reacting upon the uterus, will bring about the 

 same train of results. And thus it must be, that 

 when once the disposition to contraction is set up 

 in the uterus, whether this be from the foetus having 

 attained to a size disproportionate to the powers of 

 the mother, or from any other and accidental cause, 

 the necessary consequence will be an ever increasing 

 contraction, until the completion of birth. The his- 

 tory of gestation, therefore, so far as we can see, would 

 seem to justify the conclusion, that the contractions of 

 the uterus are owing to the withdrawal of that influ- 

 ence which the living and growing foetus exerts upon 

 this organ. 



A similar objection opposes the notion that the 

 urine stimulates contraction in the bladder; for if so, 

 how is it that the organ fills with the secretion ? On the 

 contrary, contraction takes place when an impediment 

 is opposed to the further admission of urine by the me- 

 chanical resistance of the coats of the bladder, or by the 

 antagonizing pressure of neighbouring parts, and it is 

 rather in harmony with the facts of the case, to sup- 

 pose that this phenomenon is occasioned by the want^ 

 and not by the direct operation of a stimulus. 



So far, therefore, we find no reason to suppose that 

 the changes in these muscles differ from those which 



