om, using bichloride of mercury and chloride
of lime, as already described in Chapter XV. Since, however, such
disinfection is not always practiced and since care must be taken to
avoid the introduction of the germs into the system, it is well to know
how, assuming that they have not been killed in the sick room, they make
their way from that place to a healthy individual.

_Methods of transmission of typhoid._

There are three main avenues used by the germ, namely, water, milk, and
flies, and of these three, the first is by far the most important and
includes probably 80 per cent of all the cases. The reason for this is
twofold. First, that water is so universally used, and second, that it
is so easily and generally polluted. There are many historic examples
which show definitely that water once polluted by typhoid germs is able
to spread the disease far and wide.

The epidemic in Ithaca, New York, is a good example and ranks as one of
the most serious that this country has ever known. The water-supply of
the city is taken from a small stream, Six Mile Creek, which is a
surface water with a drainage area of about 46 square miles. The stream
is polluted to a large extent. About 2000 persons live on the watershed,
and there are many houses practically on the bank of the stream which
runs for a large part of its course at the bottom of a valley with steep
side slopes. At the time of the epidemic, 1903, a dam was being built
on the stream about half a mile above the waterworks intake, and while
no proof of the fact could be found, it was generally supposed that some
of the Italians working on the dam were affected with typhoid fever and
had polluted the water. However, there were on the banks of the stream,
farther up, no less than seventeen privies, and it was known that there
were at least six cases of typhoid fever during the season just previous
to the epidemic. During the month of December, 1902, a heavy rain
occurred, so that any pollution on the banks would naturally have been
washed down into the stream. On the 11th of January, the epidemic broke
out through the town and by the middle of February there were some 600
cases reported in a population of 15,000. The number of deaths from this
epidemic was 114, and there is reason to suppose that the number of
cases was double the number reported by the physicians. After the water
from the creek was shut off and after the citizens had been persuaded to
boil all water u