familiar
scourges of the hospital, his work was perpetually putting questions to
him; to a man whose mind was open the answer might come at any moment
and from any quarter.

As a fact, already, far from his own circle and for a long while out of
his ken, there was working in France the most remarkable scientist of
the century, Louis Pasteur, who more than once put his scientific
ability at the disposal of a stricken industry, and in his quiet
laboratory revived the industrial life of a teeming population. A
manufacturer who was confronted with difficulties in making
beetroot-alcohol and was threatened with financial ruin, appealed for
his help in 1856; and Pasteur spent years on the study of fermentation,
making countless experiments to test the action of the air in the
processes of putrefaction, and coming to the conclusion that the oxygen
of the air was not responsible for them, as was widely believed. He went
further and reached a positive result. He satisfied himself that
putrefaction was set up by tiny living organisms carried in the dust of
the air, and that the process was due to what we now familiarly term
'germs' or 'microbes'. The existence of these infinitesimal creatures
was known already to scientists, but their importance was not grasped
till Pasteur, in the years 1862 to 1864, expounded the results of his
long course of studies. He himself was no expert in medicine, but his
discovery was to bear wonderful fruit when it was properly applied to
the science of health and disease. Lister's study of open wounds, his
observation of the harm done to the tissues in them when vitality was
impaired, and of the value of protective scabs when they formed, enabled
him to see the way and to point it out to others. When in 1865 he first
read the papers which Pasteur had been publishing, he found the
principle for which he had so long been searching. With what excitement
he read them, with what suddenness of conviction he accepted the
message, we do not know; he has left no record of his feelings at the
time: but it was the most important moment in his career, and the rest
of his life was spent in applying these principles to his professional
work.

With his mind thus fortified by the knowledge of the true source of the
mischief, realizing that he had to assist in a battle between the deadly
germs carried in the air and the living tissues trying to defend
themselves, Lister returned afresh to the study of methods. He