200 Proceedings of the Royal Society 
As was previously stated, the French author found that in capil- 
lary tubes of different diameter, the quantity of fluid flowing in 
equal times through equal lengths, varies not as the squares, but 
as the fourth power of the diameters. In the tubes used by us, 
in the experiment above described, the diameter was such that the 
quantities of water flowing through equal lengths were, cceteris 
paribus, as the squares of the diameters. It is interesting to 
observe in connection with experiments 43-53 inclusive, that 
whilst the amount of water flowing varied very much as the 
squares of the diameters, the quantity of blood flowing through the 
two tubes did not obey this law ; . the blood being retarded in its 
flow more than water though by no means to such an extent as 
to show that, for it, the tubes obeyed Poiseuille’s law. 
IV. On the Pressure required to force Blood Clot through Tubes of 
Narrow Diameter. 
The clot used was obtained by allowing ox’s blood to coagulate, 
and separating it from serum. 
Exp. 54. — In this experiment a tube having a diameter of IT 62 
millimetre was used. Although subjected to the whole atmo- 
spheric pressure (700 M.) none of the clot would pass through the 
tube. 
Exp. 55 and 56. — In this experiment the same clot was used, 
but a different tube. The clot was found freely to flow through 
the tube, which had a diameter of 2'00 millimetres. 
In experiment 55 the pressure of a column of mercury 24 inches 
high was employed. In experiment 56 that of a column 29 inches 
high was required. 
V. On the Rate of Flow of Milk and Urine through Narrow Tubes. 
The results of these experiments are shown in the annexed table. 
It will he observed that two tubes were employed in the determi- 
nation of the rate of flow of milk, whilst the two sets of experi- 
ments with urine were performed with one tube. The rate of flow 
of urine is shown to be almost identical with that of water, whilst 
the rate of flow of milk is about the same as that of water when a 
large tube is used, but much slower when a tube of narrow 
diameter is employed. 
