stream has a
uniform current, so that the germs are continuously carried downstream,
they will be found below the point of infection, a distance equal to
that which the stream will flow in a week. This is important because it
shows how unlikely it is that the germs once placed in water will die
out or disappear without infecting those who subsequently drink the
water. There is evidence that the typhoid germs, like all other germs
for that matter, are likely to settle to the bottom of a lake or pond,
and so a stream passing through a pond will lose a large part of the
bacterial pollution with which it entered. This is not positive enough,
however, to insure a good water-supply, since in the spring the heavy
flow of the stream will wash this deposited material out through the
pond, carrying the infectious matter downstream. In addition, the
upheaval of the settled material from the bottom of the lake, which
occurs twice a year on account of the variation in temperature at
different depths, will bring the settled germs to the top.

It has been found also that just as a high temperature destroys the
germs, so a low temperature has the same effect. Typhoid fever germs in
ice are practically harmless after two weeks, and since in natural ice
the impurities of the water are largely eliminated mechanically, so that
frozen water is purer than the water itself, there is very little
chance, even when ice is cut from a polluted pond, for typhoid germs to
be found alive after being in an ice house for three or four months. In
the ground, the life of the bacteria is longer, and while experiments do
not agree very well as to the exact length of time that the germ may
live there, there seems to be evidence that they may live several
months, if not a year or more. Cases have come under the observation of
the writer which seemed to show that certain well waters were polluted
by germs which could only have been deposited in the near-by soil nearly
a year before the time of the consequent outbreak.

Entirely to deprive the germs of life, therefore, it is necessary,
inasmuch as they are so widely distributed, to act promptly and at once
disinfect the fecal discharges from the patient rather than to wait
until those discharges have been thrown into a stream or onto the ground
and then attempt disinfection. There is probably no more important thing
in stopping the spread of typhoid fever than to practice carefully
disinfection in the sick ro