124 



THE CIRCULATION OF THE BLOOD 



our result in terms of the height to which the blood pressure could raise 

 a column of blood. 



In arteries of approximately the same size, the mean arterial blood 

 pressure does not markedly vary in different mammals. Thus, in the 

 carotid artery of the dog it averages about 110 to 120 mm. Hg, in that 

 of the eat about 105 to 115 mm., in the rabbit from 90 to 105 mm., in 

 the sheep about 150 mm., in the horse aboul 200 mm., and in man SOme- 



rig. 21. — Mercury manometer and signal magnet, arranged for recording the mean arterial 

 blood pressure in a laboratory experiment. The pressure bottle (R) is filled with anticoagulating 

 fluid and is connected by tubing with the manometer (M), the cannula for the artery (U) briny 

 connected with the T-piece (J). By this arrangement it is possible to flush out the tubing 

 when clotting interferes with the experiment. (From Jackson— Experimental Pharmacology.) 



where between 120 and 140 mm. The pressure varies in different parts 

 of the vascular system, being greatest in the aorta and least in the small- 

 est arterioles but the fall in pressure — the pressure gradient — does not 

 become very pronounced until the arterioles have become so small that 

 it is no longer possible to insert a cannula into them; thus, the mean 



