THE BLOOD. 
483 
The quantity of blood contained in an animal body may be 
made matter of speculation, but cannot, for many reasons, be 
ascertained with any degree of precision. If we attempt to draw 
all the blood out of the body, the animal sinks and dies long- 
before its vessels are evacuated ; and as we possess no means of 
measuring what remains behind, any calculation we may make 
from the quantity that has flowed must necessarily turn out vague, 
if not altogether incorrect. The following experiment will serve 
to illustrate this ; at the same time, that its result may serve as a 
datum to guide us in any future computation. 
The weight of the animal being ascertained to be 79 tb, a 
puncture was made with a lancet into the jugular vein, from 
which the blood, which flowed in a very free stream, was col¬ 
lected. The vein having ceased to bleed, the carotid artery of 
the same side was divided, but no blood came from it: in a few 
seconds afterwards the animal w r as dead. The weight of the car¬ 
cass was now found to be 73^ lb; consequently, it had sustained 
a loss of Siifo, precisely the measure of the blood drawn. It 
appears from this experiment that an animal will lose about 
1-15th part of its weight of blood before it dies; though a less 
quantity may so far debilitate the vital powers as to be, though 
less suddenly, equally fatal. In the human subject the quantity of 
blood has been computed at about 1-8 th part of the weight of the 
body; and as such an opinion has been broached from the results 
of experiments on quadrupeds, we may fairly take that to be 
about the proportion of it in the horse: so that, if w e estimate 
the weight of a common sized horse at about 12cwt., the whole 
quantity of blood will amount to 64qrts.,or 1681b, of which about 
45qrts., or 901b, will commonly flow from the jugular vein prior to 
death; though the loss of a much less quantity will sometimes de¬ 
prive the animal of life*. It is well known that young animals 
possess more blood than old, and that they will, perhaps, on 
this account, sustain greater bodily injuries, and bear larger 
hemorrhages; indeed, they are wisely provided with such an ex¬ 
cess, if we may so term it, in order that their growth may be 
promoted, and their several organs maintained in a state of vi- 
* Supposing a man to weigh 12st., or 168ft, the quantity of blood con¬ 
tained in his body may be rated at 21 lb, or 2gall. 2qrts. and 1 pint. Again, 
granting that a dog weighs 401b, the amount of his blood will be 5 pints. 
These calculations are useful and worth our attention, inasmuch as they 
serve to guide us in practice, as to the probable extent to which we may, 
with safety, carry venesection in different animals. For instance, we may 
reckon the loss of a pint from a man to be equivalent to that of a gallon 
from a horse, or to four ounces from a dog, and vice versa; selecting in¬ 
dividuals from each class about the respective weights we have here set 
down. 
