REMARKS ON COMPOSITION OF THE BLOOD, 607 
lating fluids compose no less than a third part of the weight 
ot the individual animal, and that all the so-called solid parts 
of the frame were at one time in a state of fluidity. The 
fluids met with are various, consisting chiefly of the blood, 
the lymph, the chyle, and the different secretions. The 
latter named, as well as the lymph, depend immediately on 
the blood itself for their existence, while this, in its turn, 
has its chief source in the chyle—the fluid which is produced 
in the animal organism by the processes of digestion and 
assimilation of the food on which the creature subsists. The 
several changes which the food undergoes before it becomes 
converted into chyle have been fully set forth in the lecture 
before referred to, and this being the case it will be only 
necessary to direct the reader’s attention to the explanations 
therein given. 
In comparing the quantity of blood with the entire weight 
of an animal, it will be found difficult to arrive at the exact 
proportion they relatively hold to each other, but it is suffi¬ 
cient for our present purpose to state that the amount is 
usually estimated at from one fourth to one fifth of the entire 
* 
weight of the body. 
If we were to attempt to give a popular definition of the 
blood, it might be described as a fluid which circulates 
through the heart, arteries, and veins, carrying with it the 
materials which are indispensably necessary for the mainte¬ 
nance of life, heat, nutrition, renovation, and secretion, building 
up the organism of the young animal and supporting that of 
the adult and aged. To effect the passage of the blood from 
one part of the system to another, various organs are employed 
and several forces brought into operation. The chief organ 
for this purpose is the heart, which may be regarded as a 
central pump, having in connection with it two sets of 
vessels—the arteries and veins—the former of these being 
transmitting, and the latter returning conduits. Besides 
these vessels there are intermediately placed between them, 
as it were, another set, called, from their small size, capil¬ 
laries, to which we shall have occasion, hereafter, more par¬ 
ticularly to allude. 
It is well known that in all the higher orders of vertebrate 
animals, the blood, as it appears to the unassisted vision, 
when drawn from its vessels, is red in colour. This redness, 
however, does not depend on any inherent colour in the 
fluid itself, but is due to an innumerable number of red cor¬ 
puscles or cells which are floating within it. If, then, these 
bodies are removed from the blood, the true liquor sanguinis 
which remains behind will be found to be of a pale straw 
