7 
of the Heart and Arteries. 
water would rise, in a tube fixed laterally into the artery, is 
only two inches less than in the immediate neighbourhood of 
the heart. 
In order to judge of the comparative resistance produced 
by fluids of different degrees of viscidity, I employed the 
same tubes, by means of which I had determined the friction 
of water, in extreme cases, for ascertaining the effect of dif- 
ferent substances held in solution in the water : since it is 
impossible to make direct experiments on the blood in its na- 
tural state, on account of its tendency to coagulate : and those 
substances which have the power of preventing its coagula- 
tion, may naturally be supposed to produce a material change 
in its viscidity. The diameter of one of the tubes, which was 
cylindrical, was the fortieth part of an inch : the bore of the 
other was oval, as is usual in the finest tubes made for ther- 
mometers : the section, divided by one fourth of the circum- 
ference, gave one hundred and seventy seconds for the mean 
diameter. I caused some milk, and solutions of sugar of dif- 
ferent strength, to pass through these tubes : they were all 
transmitted much more sparingly than water, with an equal 
pressure, and the difference was more considerable in the 
smaller than in the larger tube, as might naturally be expected 
both from the nature of the resistance, and from the result of 
Gerstner's experiments on water at different temperatures. 
In the first tube the resistance to the motion of milk was 
three times as great as to that of water, a solution of sugar in 
five times its weight of water produced twice as much resist- 
ance as water ; in twice its weight, nearly four times as much 
as water : but in the narrower tube, the weaker solution of 
sugar exhibited a resistance five times as great as that of 
