ered at the time which centuries of experience
has shown us to be the most effective, between or shortly before the
paroxysms, it either prevented sporulation or killed the spores. So that
at one triumphant stroke the mystery of centuries was cleared up.

But here will challenge some twentieth-century _Gradgrind_: "This is all
very pretty from the point of view of abstract science, but what is the
practical value of it? The discovery of the plasmodium and its
peculiarities has merely shown us the how and the why of a fact that we
had known well and utilized for centuries, namely, that quinine will
cure malaria." Just listen to what follows. The story of the plasmodium
is one of the most beautiful illustrations of the fact that there is no
such thing as useless or unpractical knowledge. The only thing that
makes any knowledge unpractical is our more or less temporary ignorance
of how to apply it. The first question which instantly raised itself
was, "How did the plasmodium get into human blood?" The very
sickle-shape of the plasmodium turned itself into an interrogation mark.
The first clew that was given was the new and interesting one that this
organism was a new departure in the germ line in that it was an animal,
instead of a plant, like all the other hitherto known bacilli, bacteria,
and other disease-germs.

It may be remarked in passing that its discovery had another incidental
practical lesson of enormous value, and that was that it paved the way
for the identification of a whole class of animal parasites causing
infectious diseases, which already includes the organisms of Texas fever
in cattle, dourine in horses, the _tsetse_ fly disease, the dreaded
sleeping sickness, and finally such world-renowned plagues as syphilis
and perhaps smallpox.

Being an animal, the plasmodium naturally would not grow upon
culture-media like the vegetable bacilli and bacteria, and this very
fact had delayed its recognition, but raised at once the probability
that it must be conveyed into the human body by some other animal.
Obviously, the only animals that bite our human species with sufficient
frequency and regularity to act as transmitters of such a common disease
are those Ishmaelites of the animal world, the insects. As all the
evidence pointed toward malaria being contracted in the open air,
attested by its popular though unscientific name _mal-aria_, "bad air,"
and as of all forms of "bad air" the night air was incomparably