, the
temperature, humidity, direction of wind, barometric pressure, and
electric tension, is in succession the principal cause of the spread of
this plague. Many interesting coincidences were shown. But one thing
always puzzled us, and that was, that the heaviest mortality usually
occurred, not just at the beginning of winter, when the shock of the
cold would be severest, nor even in the months of lowest temperature,
like December or January, but in the late winter and the early spring.
Throughout the greater part of the temperate zone the death-rate for
pneumonia begins to rise in December, increases in January, goes higher
still in February, reaching its climax in that month or in March. April
is almost as bad, and the decline often doesn't fairly set in until May.

No better illustration could probably be given of the danger of drawing
conclusions when you are not in possession of all the facts. One thing
was entirely overlooked in all this speculation until about twenty years
ago,--that pneumonia was due not simply to the depressing effects of
cold, but to a specific germ, the pneumococcus of Fraenkel. This threw
an entirely new light upon our elaborate weather-causation theories. And
while these still hold the field by weight of authority and that mental
inertia which we term conservatism, yet the more thoughtful physicians
and pathologists are now coming to regard these factors as chiefly
important according to the extent to which we are crowded together in
often badly lighted and ill-ventilated houses and rooms, with the
windows and doors shut to save fuel, thus affording a magnificent
hothouse hatching-ground for such germs as may be present, and ideal
facilities for their communication from one victim to another. At the
same time, by this crowding and the cutting off of life and exercise in
the open air which accompanies it, the resisting power of our bodies is
lowered. And when these two processes have had an opportunity of
progressing side by side for from two to three months; when, in other
words, the soil has been carefully prepared, the seed sown, and the
moist heat applied as in a forcing-house, then we suddenly reap the
harvest. In other words, the heavy crop of pneumonia in January,
February, and March is the logical result of the seed-sowing and forcing
of the preceding two or three months.

The warmth of summer is even more depressing in its immediate effects
than the cold of winter, but the heat ca