496 On Auxiliary Forces concerned in the Circulation [Apr. 24, 



that area. If it were not so, and but the pushing forward of the mass, 

 no difference wonld exist, and, consequently, no reading obtained. 

 And this is proved by observing the effect on tLe readings when the 

 uterine contractions occur, to which I alluded at the commencement 

 of this note ; for, when these supervene, we find the respiratory 

 readings reduced almost to nothing, and, instead of the high elevation 

 waves of the tracing, well shown before, the line is nearly level. 

 Thus, when the uterus, in consequence of the increased firmness of its 

 walls, cannot be impressed nor can bulge, we have the effect of the 

 descent of the diaphragm to a similar extent reduced. This being 

 admitted, it is clear that every respiratory action causes a movement 

 of the fluids contained within the uterus, thus assisting the circulation 

 in a part apparently removed from the maternal cardiac impetus. It 

 may be worthy of notice, that at the earlier period of pregnancy, the 

 uterine walls are less yielding, and, therefore, less influenced by the 

 respiratory act, but then the assistance this renders at a later period is 

 not so much required, because neither are the sinuses so large nor the 

 decidual processes with their sinuses so deep, nor the thickness of the 

 placenta so great. Gradually as the uterus increases, its walls are 

 more yielding and the force of the respiratory movement more felt 

 within. 





l ^- // ~^~~~ r ^~~ uterhrte. 



contraction-. 



con.tra.ctio 



n, suiys idxru^ . 







coritra-ctiui 



x. -pets sect oJJ\ 



The effects of Uterine Contractions during Pregnancy in reducing the height of the 

 Respiratory Wave is seen by comparing the first line with the last. This tracing 

 was taken with a smaller instrument. 



There are other points of interest in this registration of the 

 respiratory movements of the abdomen, which do not belong to the . 

 subject under consideration, and are, therefore, omitted here. 



But there are other accessory forces to be noticed which act on the 

 surface of the pregnant uterus, tending to the movement of the fluids 

 within ; namely, the muscular movements of the body, tending to 

 cause a change of shape of the thorax or abdomen. These are 

 quickly shown by the same arrangements as that by which the 

 ordinary respiration is shown. The elevation of the arm, a hoist of 

 the body, and, in particular, coughing, show a much greater force than 

 is exerted by inspiration. Hence, one might fairly infer that exercise 



