a week or two.

An interesting epidemic occurred in Massachusetts, caused by a farmer's
boots carrying infectious matter from recently manured fields onto the
well cover, whence it was washed into the well by repeated pumping.

The moral of these incidents is very plain, namely, that where any
possibility of the infection of drinking water occurs, that water ought
either to be avoided or else to be thoroughly sterilized before using.
This applies particularly to the old-fashioned well,--the kind with
loose board covers and chain pumps.

_Construction of wells in reference to typhoid._

Two points already mentioned are essential if well water is to be kept
pure. One is to line the well with a water-tight masonry lining, and the
other point is to have the cover of the well made with a thoroughly
water-tight coating. This does not always give full protection, since
in some cases polluting matter may pass through even ten feet of soil.
This would be particularly true if the well was in a fissured or seamed
rock, and very recently the writer found a well dug in a laminated
granite, where a near-by sewer, leaking at the joints, contaminated the
water of the well, although the well was cased with an iron casing
twenty-five feet deep. The sewage escaped into a crack in the rock and
followed the crack down vertically and horizontally into the well.
Limestone is even more dangerous if any pollution exists in the
vicinity. In cases where a well goes down to a horizontal layer of
limestone and where a privy vault is dug to the same rock, it is found
that pollution will follow the surface of the rock horizontally a long
distance, and this condition of things always makes a well water
suspicious. In sand or fine gravel, on the other hand, the danger of
contamination is almost negligible; on Long Island, for example, the
cesspools and well are both dug ten or fifteen feet deep and only fifty
feet apart without any trace of contamination being detected.

_Milk infection by typhoid._

Milk is responsible for perhaps 5 per cent of the cases of infection.
Although the infection is always foreign to the milk itself,--that is,
enters the milk only after the milk is drawn from the cow,--milk
frequently becomes infected because infected water has been added to it
or because the cans have been washed in infected water, or because some
persons in contact with a typhoid patient have had their hands infected
and then handled the milk or th