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 overthrow of Stahl's
famous theory and the establishment of modern chemistry, we must review
the work of another great chemist, Karl Wilhelm Scheele (1742-1786), of
Sweden, who discovered oxygen quite independently, although later than
Priestley. In the matter of brilliant discoveries in a brief space of
time Scheele probably eclipsed all his great contemporaries. He had a
veritable genius for interpreting chemical reactions and discovering
new substances, in this respect rivalling Priestley himself. Unlike
Priestley, however, he planned all his experiments along the lines of
definite theories from the beginning, the results obtained being the
logical outcome of a predetermined plan.

Scheele was the son of a merchant of Stralsund, Pomerania, which then
belonged to Sweden. As a boy in school he showed so little aptitude for
the study of languages that he was apprenticed to an apothecary at the
age of fourteen. In this work he became at once greatly interested, and,
when not attending to his duties in the dispensary, he was busy day and
night making experiments or studying books on chemistry. In 1775, still
employed as an apothecary, he moved to Stockholm, and soon after he sent
to Bergman, the leadi