are more precise it is still
known as the _Diplococcus pneumoniae_ or _Diplococcus lanceolatus_, from
its faculty of usually appearing in pairs, and from its lance-like
shape. Its conduct abounds in "ways that are dark and tricks that are
vain," whose elucidation throws a flood of light upon a number of
interesting problems in the spread of disease.

First of all, it literally fulfills the prognostic of Scripture, that "a
man's foes shall be they of his own household," for its chosen abiding
place and normal habitat is no less intimate a place than the human
mouth. Outside of this warm and sheltering fold it perishes quickly, as
cold, sunlight, and dryness are alike fatal to it.

We could hardly believe the evidence of our senses when studies of the
saliva of perfectly healthy individuals showed this deadly little
bacillus to be present in considerable numbers in from fifteen to
forty-five per cent of the cases examined. Why, then, does not every one
develop pneumonia? The answer to this strikes the keynote of our modern
knowledge of infectious disease, namely, that while an invading germ is
necessary, a certain breaking down of the body defenses and a lowering
of the vital resistance are equally necessary. These invaders lie in
wait at the very gates of the citadel, below the muzzles of our guns, as
it were, waiting for some slackening of discipline or of watchfulness to
rush in and put the fortress to sack. Nowhere is this more strikingly
true than in pneumonia. It is emphatically a disease where, in the
language of the brilliant pathologist-philosopher Moxon, "While it is
most important to know what kind of a disease the patient has got, it is
even more important to know what kind of a patient the disease has got."

The death-rate in pneumonia is an almost mathematically accurate
deduction from the age, vigor, and nutrition of the patient attacked. No
other disease has such a brutal and inveterate habit of killing the
weaklings. The half-stifled baby in the tenement, the underfed,
overworked laboring man, the old man with rigid arteries and stiffening
muscles or waning life vigor, the chronic sufferer from malnutrition,
alcoholism, Bright's disease, heart disease--_these_ are its chosen
victims.

Another interesting feature about the pneumococcus is its vitality
outside of the body. If the saliva in which it is contained be kept
moist, and not exposed to the direct sunlight and in a fairly warm place,
it may sur