that he
can set his teeth into. But his tissues are still swarming with the
bacilli, and any indiscretion, either of diet, exposure, or exertion, at
this time, may result in forming a secondary colony, or abscess,
somewhere in the lungs, the liver, or the muscles. He must be kept quiet
and warm, and abundantly, but judiciously, fed, for at least three
weeks after the disappearance of the fever, if he wishes to avoid the
thousand and one ambuscades set by the retreating enemy.

Now, what has happened when recovery begins? One would suppose that
either the bacilli had poisoned themselves, exhausted the supplies of
nourishment in the body of the patient, so that the fever had "burnt
itself out," as we used to say, or that the tissues had rallied from the
attack and destroyed or thrown out the invaders. But, on the contrary,
we find that our convalescent patient, even after he is up and walking
about, is still full of the bacilli.

To put it very crudely, what has really happened is that the body has
succeeded in forming such antidotes against the poison of the bacilli
that, although they may be present in enormous numbers, they can no
longer produce any injurious effect. In other words, it has acquired
immunity against this particular germ and its toxin. In fact, one of our
newest and most reliable tests for the disease consists in a curious
"clumping" or paralyzing power over cultures of the _Bacillus typhosus_,
shown by a drop of the patient's blood, even as early as the seventh or
eighth day of the illness. And, while it is an immensely difficult and
complicated subject, we are justified in saying that this immunity is
not merely a substance formed in the body, the stock of which will
shortly become exhausted, but a faculty acquired by the body-cells,
which they will retain, like other results of education, for years, and
even for life. When once the body has learned the wrestling trick of
throwing and vanquishing a particular germ or bacillus, it no longer
has much to dread from that germ. This is why the same individual is
seldom attacked the second time by scarlet fever, measles, typhoid, and
smallpox.

While, however, the individual may be entirely immune to the germs of a
given disease, he may carry them in his body in enormous numbers, and
infect others while escaping himself.

This is peculiarly true of typhoid, and we are beginning to extend our
sanitary care over recovered patients, not merely to the end of