one large artery, whose main trunk distributes the blood into its
lesser branches, and thence through the capillaries. Cutting off
this main artery, it would seem, should cut off entirely the
blood-supply to the particular organ which is supplied by this
vessel; and until the time of Hunter's demonstration this belief
was held by most physiologists. But nature has made a provision
for this possible stoppage of blood-supply from a single source,
and has so arranged that some of the small arterial branches
coming from the main supply-trunk are connected with other
arterial branches coming from some other supply-trunk. Under
normal conditions the main arterial trunks supply their
respective organs, the little connecting arterioles playing an
insignificant part. But let the main supply-trunk be cut off or
stopped for whatever reason, and a remarkable thing takes place.
The little connecting branches begin at once to enlarge and draw
blood from the neighboring uninjured 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