12 



and if this means anything it means that circulation shall be in correspondence 

 with the physiological requirements, or supply equal to demand, the cardinal 

 circumstance being the </i-t/1/i and elaboration <>f the embryo, which is the object 

 and purpose of the organ, the others being simply incidental. 



It conies to this, namely, that the nervous force for expanding and contracting 

 the uterine sinuses should expand and contract the uterine bloodvessels at one 

 and f/ie n<une time, thereby causing afflux and efflux of blood through them for 

 compelling correspondence throughout which the scheme calls for. Furthermore, 

 this wou'd accord with the action in the vessels in respiration, as indicated 

 by the undulations in arterial tension. But would not this mechanics inter- 

 fere with the due circulation of blood in the placental sinuses'? Certainly 

 not, and for the following reasons : 1. Efflux of blood through the veins 

 is by means of capillary vessels, which tend to retard escape, while the flow of 

 blood in and out the placenta] sinuses takes place through large canals (Fig. 

 5, c,c, c, r). But in addition to this, the expansion in the placenta, which occurs 

 during systole of the womb, should also determine the blood in this direction. 



2. During diastole in the womb and its sinuses, for aspirating the placental 

 sinuses, the hic/h j-i'xsuri- in the arterial system causes this blood to flow into 

 the uterine sinuses as rapidly as the blood coming from the placenta ; at the 

 same time, the valves in the veins of the uterus obviate reflux from the venous 

 a- if stem. When the womb contracts for compelling the blood in the placenta 

 and venous system, the pressure in the arterial inhibits reflux in this direction. 

 Thus the mechanics for increasing circulation in the uterine and placental 

 sinuses is complete in every respect, nor does it require extensive expansion and 

 contraction in the womb in order to effect increased circulation through the 

 sinuses, but a moderate and limited amount, sufficient only for producing 

 rhythmical changes in pressure upon Hie blood, as must appear obvious : some- 

 thing similar to what takes place in the spongiic, which have muscles (Norway) 

 for producing a more rapid circulation in and out this canal system. 



Tltis expansion of the irouJ) and arterial feeders would explain the sudden and 

 enormous escape of arterial blood in post partem haemorrhage, for the placenta 

 being no longer attached, the flow of blood through the uterine sinuses must 

 necessarily be purely arterial. In other words, when contraction ceases and 

 the movement of expansion sets in, the flood-gates are thrown open to the 

 arterial system. 



In reference to the nervous centre for this pumping action in the womb, 

 which answers to respiration in the foetus. There can be very little doubt 

 but that the spinal-cord functions as the common reflex centre of nervous force 

 for producing the rhythmical expansions and contractions in the gravid womb 

 simulating respiration. The following are the reasons for this allegation : 1. 

 The very intimate connection subsisting between the womb and spinal cord by 

 means of the hypogastric ganglia and sacral plexus with the intercommunicating 

 nerves. 2. The fact that the lumbar portion of the spinal cord undergoes en- 

 largement during gestation (Mathews Duncan). 3. The fact that reflex action in 

 the womb is readily produced by applications to the skin surface, a circumstance 

 well known and practised by the profession. All these facts fall readily 



