light. Huxley's pessimistic saying that
typhoid was like a fight in the dark between the disease and the
patient, and the doctor like a man with a club striking into the melee,
sometimes hitting the disease and sometimes the patient, is no longer
true since the birth of bacteriology.

Nowhere can the natural history of disease be more clearly seen or more
advantageously studied than in the case of typhoid fever.

The cause of typhoid is simplicity itself, merely drinking the excreta
of some one else, "eating dirt," in the popular phrase; simple, but of a
deadly effectiveness, and disgracefully common. The demon may be
exorcised by an incantation of one sentence: _Keep human excreta out of
the drinking water._ This sounds simple, but it is n't. Eternal
vigilance is the price of health as well as of liberty.

We can, however, make our pedigree of typhoid a little more precise. It
is not merely dirt of human origin which is injurious, but dirt of a
particular type, namely, discharges from a previous case of the disease.
Just as in the fight against malaria we have not the enormous problem of
the extermination of all varieties of mosquito, but only of one
particular genus, and only the infected specimens of that, so in
typhoid, the contamination of water or food which we have to guard
against is that from previous cases. From one point of view, this leaves
the problem as wide as ever, for, obviously, the only way to insure
against poisoning of water by typhoid discharges is to shut out
absolutely all sewage contamination. On the other hand, it is of immense
advantage in this regard,--it enables us to fight the enemy at both ends
of the line, to turn his flank as well as crush his centre.

While we are protecting our water-supplies against sewage, we can, in
the meantime, render that sewage comparatively harmless by thoroughly
disinfecting and sterilizing all discharges from every known case of the
disease. A similar method is used in the fight against yellow fever and
malaria. Not only are the breeding places of the two mosquito criminals
broken up, but each known case of the disease is carefully screened, _so
as to prevent the insects from becoming infected_, and thus able to
transmit the disease to other human victims.

It cannot be too emphatically insisted upon that every case of typhoid,
like every case of yellow fever and of malaria, _comes from a previous
case_. It is neither healthy nor exhilarating to drink a c