these experiments see that though pure dephlogisticated air might
be useful as a medicine, it might not be so proper for us in the
usual healthy state of the body."

This suggestion as to the possible usefulness of oxygen as a
medicine was prophetic. A century later the use of oxygen had
become a matter of routine practice with many physicians. Even in
Priestley's own time such men as Dr. John Hunter expressed their
belief in its efficacy in certain conditions, as we shall see,
but its value in medicine was not fully appreciated until several
generations later.

Several years after discovering oxygen Priestley thus summarized
its properties: "It is this ingredient in the atmospheric air
that enables it to support combustion and animal life. By means
of it most intense heat may be produced, and in the purest of it
animals will live nearly five times as long as in an equal
quantity of atmospheric air. In respiration, part of this air,
passing the membranes of the lungs, unites with the blood and
imparts to it its florid color, while the remainder, uniting with
phlogiston exhaled from venous blood, forms mixed air. It is
dephlogisticated air combined with water that enables fishes to
live in it."[5]


KARL WILHELM SCHEELE

The discovery of oxygen was the last but most important blow to
the tottering phlogiston theory, though Priestley himself would
not admit it. But before considering the final steps in the