190 Transactions of the Canadian Institute. [Vol. VII. 



carotid artery. The animals were all under the influence of some 

 anaesthetic, the nature of which is mentioned when necessary ; but as 

 the effects of posture were more or less the same in all cases, it may 

 be inferred that they were not due to the anaesthetic, except as regards 

 degree. As a rule some morphia was first given hypodermically, and 

 then very little chloroform sufficed to keep them quiet. 



Tracing 3 is from a dog under chloroform. Where the tracing begins 

 he is horizontal, and the canula is in the carotid. At i the hind feet 

 were suddenly lowered, and the pressure is seen to markedly fall. When 

 placed horizontal again at 2 the pressure rapidly rose and went above 

 the normal for a short time, 3, and then resumed the normal line. This 

 is a very constant feature in such tracings, and is probably due partly to 

 inertia, and partly to the compensation which has been taking place 



""^■■^.^X^ 



Tracing III.— 1/3. — Normal effects ot gravity on carotid blood pressure. Dog under Chlorotorm. 

 I Animal placed vertical (feet downwards). 2 Horizontal again. 3 Compensation continuing. 4 Head 

 downwards. 5 Horizontal again . 



against the effect of the vertical position still continuing after the animal 

 is again horizontal. This compensation, as we shall see, is partly 

 affected by increase in the rate of the heart-beat and partly by 

 constriction of the arteries, while contraction of the abdominal wall is 

 also of service here. ^ At 4 the animal was suddenly placed in the 

 vertical feet-up posture, and at once the carotid pressure rose. This 

 rise was not so great as the fall which occurred in the feet-down posture, 

 and a rule may be deduced that t/ie lozvering of a pole of the body does 

 not raise the arterial blood pressure in it so much as raisijig that pole 

 lowers it. 



When placed horizontal at 5 the pressure fell below the normal line 

 for the same reasons that it rose above that line at 3. 



Some dogs are not nearly so susceptible to the effects of gravity as 



I " Influence of Gravity on the Circulation." Hill and Barnard. Journal of Physiology, Vol. XXI., 

 1S97. 



