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. This was the beginning of what we call _vaccination_; and as soon as it was found that this scratching of the arm and putting a little of this _vaccine_ matter into it would cause only a few days of feverishness, and then after that give complete protection against smallpox, the Boards of Health all over the civilized world took it up and insisted upon everybody's being vaccinated when a baby. As a result, smallpox has become one of the rarest, instead of the commonest, of our infectious diseases. Only a few dozen people die of it each year in Europe, instead of several hundred thousands; scarcely one one-hundredth of the people now in our blind asylums have been sent there by smallpox, and I dare say that many of you have never even seen a pock-marked person. Another disease that used to be very dangerous to little children is _diphtheria_. It was not only very infectious, but very deadly; and nearly half of the children who took it died of it, and the doctors didn't know anything that would cure it. About twenty years ago, two great scientists, one a Frenchman named Roux--a student of the great Professor Louis Pasteur, of whom I am sure you have heard--and the other, a German, named Behring, discovered an _antitoxin_ for diphtheria; that is, something to defeat the poison of the diphtheria germ. When this antitoxin is injected into the blood, it will cure diphtheria. The doctors and the Boards of Health took this up too, and insisted upon its being used in all cases; with the result that where the antitoxin is used early, scarcely one in twenty of the patients dies, instead of eight or ten out of twenty, as before.