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Transactions of the Canadian Lnstitltk. 



[Vol. VII. 



position. At 14 it was swung into the vertical feet-up position, and a 

 slight fall occurred. 



So much for the changes in pressure uninfluenced as far as possible 

 by anything except posture. I next proceed to the effects of certain 

 factors in increasing and decreasing the blood pressure, and its suscepti- 

 bility to gravity and inertia. 



Abdominal Pressure. 



Tracings 10 and 11 show the effect of firm abdominal pressure in 

 raising the blood pressure while this is low from the animal being in the 

 vertical posture. In 11 the vertical position assumed at 18 produced a 

 slight fall, and abdominal pressure applied at 19 raised the tracing to 



Tracing X. — 3/10. — 3 Vertical. Pressure continued to fall. 4 Abdominal pressure. 5 A pressure 

 removed. 6 Horizont.il. 



\ 



ly 10 



Tracing XI. — 1/2. — 18 Vertical. 19 Abdominal pressure. 20 Horizontal. 



even above the normal line. In the former tracing the pulse was 

 hastened by the abdominal pressure, in the latter it remained unaltered. 



Abdominal pressure, however, in order to be effectual, must be of an 

 exceedingly firm nature, and probably pressure upon the aorta itself has 

 something to do with the result. It has been shown indeed that when 

 the aorta is compressed by itself a marked rise in the general blood 

 pressure occurs^ Far more abdominal pressure is necessary than would 

 be required merely to empty the abdominal veins — this being the usual 

 explanation of how the resulting rise in blood pressure is brought about. 



I J. A. McWilliams, British Medical Journal, \'ol, II., 1890, p. 835. 



