ed
supply-trunk, This enlargement continues until at last a new route for
the circulation has been established, the organ no longer depending
on the now defunct original arterial trunk, but getting on as well as
before by this "collateral" circulation that has been established.

The thorough understanding of this collateral circulation is one of the
most important steps in surgery, for until it was discovered amputations
were thought necessary in such cases as those involving the artery
supplying a leg or arm, since it was supposed that, the artery being
stopped, death of the limb and the subsequent necessity for amputation
were sure to follow. Hunter solved this problem by a single operation
upon a deer, and his practicality as a surgeon led him soon after to
apply this knowledge to a certain class of surgical cases in a most
revolutionary and satisfactory manner.

What led to Hunter's far-reaching discovery was his investigation as to
the cause of the growth of the antlers of the deer. Wishing to ascertain
just what part the blood-supply on the opposite sides of the neck played
in the process of development, or, perhaps more correctly, to see what
effect cutting off the main blood-supply would have, Hunter had one of
the deer of Richmond Park caught and tied, while he placed a ligature
around one of the carotid arteries--one of the two principal arteries
that supply the head with blood. He observed that shortly after this the
antler (which was only half grown and consequently very vascular) on the
side of the obliterated artery became cold to the touch--from the lack
of warmth-giving blood. There was nothing unexpected in this, and Hunter
thought nothing of it until a few days later, when he found, to his
surprise, that the antler had become as warm as its fellow, and was
apparently increasing in size. Puzzled as to how this could be, and
suspecting that in some way his ligature around the artery had not been
effective, he ordered the deer killed, and on examination was astonished
to find that while his ligature had completely shut off the blood-supply
from the source of that carotid artery, the smaller arteries had become
enlarged so as to supply the antler with blood as well as ever, only by
a different route.

Hunter soon had a chance to make a practical application of the
knowledge thus acquired. This was a case of popliteal aneurism,
operations for which had heretofore proved pretty uniformly fatal. An
aneuris