Page 12, 
Page 12. 
52 THE LAW WHICH REGULATES 
insulation of long cables at different times occurred to me as being 
subject to exactly similar laws, the time of fall of cable charge from 
tension to half tension, which he employs, varying directly as the 
leakage, and as that only. 
Can it be that the heart always recommences to beat when the 
tension falls a certain invariable proportion, and then only? This 
theory it was my next object to analyse, and the different elements 
into which it resolves itself were, and will be now, considered sepa- 
rately. Sao m 
First, as to the full meaning of the term—a uniform ‘insulation. 
A uniform circulation is one in which the quantity of fluid flowing 
through all cross sections of the circulating system is the same; for 
if the flow through one part were less than through another, there 
would be a tendency for the fluid to accumulate in front of the obstruc- 
tion, which is incompatible with the premises. 
As a consequence of this, the heart must always recommence to 
beat directly as much blood has left the capillaries as was sent out 
from it in the previous pulsation, and therefore the length of the pause 
or diastole must depend on the relative capacities of the heart and of 
the arterial system, and on the rapidity of the flow of blood through 
the capillaries. 
At this point the work of Poiseuille respecting the flow of fluids 
through capillary tubes is invaluable. He found* that, other things 
being the same, the flow of fluids through capillary tubes varies 
directly as the pressure. These results were verified by a Committee 
of the Academy of Sciences; and by an entirely different method I 
have been enabled to do the same on the vessels of the animal system. 
My method was the following in a particular case :—The kidneys 
of a deer, with the aorta and renal vessels intact, were removed from 
its body and placed for some time in water at 100° F.; the aorta was 
ligatured just below the origin of the renal arteries, and a uniform 
glass tube was tied into it just above them. Water at 100° F. was 
poured into the tube and it distended the organs; the tube was main- 
tained full by a continuous supply, which was suddenly stopped and 
the time of fall of the column from tension to half tension at different 
initial pressures observed, and it was always found that it took exactly 
the same time to fall from 40 inches to 20 inches as from 20 inches to 
10 inches, thus verifying the law. 
This law being thus true, it is evident that if the capacity of the 
arterial system, including the left ventricle, varies directly as the 
* “ Recherches expérimentales sur le mouvement des liquides dans les tubes de 
trés-petits diamétres.”” ‘ Rapport de l’Académie des Sciences. Comptes Rendus.” 
Tome IV. 1842. 
