or several of the limbs of an animal, so as to
interrupt both the arterial and venous circulation.

The proof and explanation of this may be thus presented:

In the first place, it is well known that children and small animals
are affected by much smaller quantities of anaesthetics and other
medicinal substances than are required to produce equal effects in men
and large animals.

At first sight, there appears to exist a certain definite relation
between the weight of the animal and the quantity of medicament
required to produce physiological effects. On closer inquiry, however,
we find behind this proposition the deeper truth that the real
proportion is between the magnitude of the blood-mass and the amount
of medicament. Thus, if we withdraw a considerable amount of blood
from a large dog, we may be able to affect him by much smaller doses
than those required under ordinary circumstances; and, among human
beings, we find the anaemic much more susceptible to remedies than the
full-blooded of equal weight.

The degree of saturation of the blood-mass with the remedy is
obviously, then, the principal thing; the greater the amount of blood,
the more remedy--everything else being equal--we shall have to give in
order to obtain definite results.

If we wish to embody the proposition in a mathematical statement, we
may do so in the following simple manner:

Let a represent the total quantity of blood, _b_, the amount of remedy
exhibited, and _x_ the magnitude of the physiological effect. We shall
then have the simple formula, x = b / a.

Again, if we withdraw a certain quantity of blood from the circulation
by venesection, and call that amount _d_, we shall then have the
formula x = b / (a-d).

But, if we wish to act upon the organs of the trunk, and more
especially upon those contained within the cerebro-spinal canal, it is
not necessary to resort to such a drastic expedient as copious
blood-letting; for, in place of this, we may dam up and effectually
eliminate from the rest of the body a certain amount of blood by
passing a ligature around the central portion of one or several
extremities, so as to interrupt the circulation in both artery and
vein. When this has been done it is clear that we may introduce a
remedy into the system by way of the stomach, or hypodermically into
some portion of the trunk; and it is equally certain that a remedy so
introduced will be diluted only in the ratio of the amount of blood
f