obey all their rules; and perhaps when you don't know what the dangers
are which they are trying to guard you against, it seems to you that
they are too particular about a great many things. But just see what
they have done already to make our cities and houses healthier and
pleasanter places to live in.

Only one hundred and fifty years ago, for instance, that terrible
disease called _smallpox_ killed hundreds of thousands of people every
year in Europe; and it attacked the eyes and blinded so many of those
who recovered from it, that nearly half the poor blind people in the
blind asylums had had their sight destroyed by it. In smallpox there
is a terrible eruption, or breaking out, upon the skin, which is
likely to leave it pitted and scarred; and even fifty years ago it was
exceedingly common to see people who had been pitted by smallpox, or,
as the expression was, "pock-marked."

Cows have a disease somewhat like this, but much less dangerous,
called cow-pox. Years ago, before dairies were inspected as they are
now, dairy maids often caught this disease from the cows they milked,
so that their hands would break out with pock-marks.

About a hundred years ago, a Dr. Richard Jenner discovered that the
dairy maids in the country district in which he lived, who had caught
this mild infection from the cows they milked, never caught smallpox
even when they were exposed to it. So after studying over the subject
for some years, he took a little of the matter, or pus, from the
eruption on the udder of a cow that had cow-pox, scratched the arm of
a little patient of his, and rubbed some of the pus into it. Only a
short time after, the family of this little boy was exposed to
smallpox, and all the other children took it badly, but he escaped.