We now come to the study of a disease, the cause of which has not been positively recognized. We know that it is very communicable; but we know also that there is absolutely no reason for anyone's ever contracting it, since there is a way by which it may easily be prevented. [Sidenote: Fatality of smallpox before the discovery of vaccination] Something over a hundred years ago, smallpox was one of the most fatal diseases known. It is estimated that during the eighteenth century it killed over 60,000,000 people. Up to the time when the Spaniards invaded Mexico, there had been no smallpox there. The Spaniards brought the disease with them, and historians tell us that out of the 12,000,000 people living in Mexico at that time, at least 6,000,000 died from smallpox. At that time the disease was considered fatal throughout the world; when it broke out in a community, people fled without stopping to bury their dead. It was a rare thing to see a person not more or less disfigured by the marks the disease leaves on the face and body. To-day we find a very different condition. There are now fewer fatalities from smallpox than from almost any other communicable disease. During 1906 and 1907 only 169 deaths from smallpox were reported from all over the United States to the Census Bureau at Washington. What has caused this marked falling off in the fatality of the disease? [Sidenote: Discovery of vaccination] During the time that smallpox was killing so many people, all the doctors were trying to find something that would cure the disease or that would prevent it. In the latter part of the eighteenth century Dr. Edward Jenner, an English physician, noticed that milkmaids did not have smallpox as much as did people of other occupations. He also noticed cows with little sores on their udders that looked very much like the sores that come with smallpox. He therefore tried making on the arms of people sores just like those on the udders of the cows. He did this by taking a little of the matter from the sores on the cows and putting it into the scratches on the people's arms. After these sores had healed, the people who had been thus treated did not have smallpox. This simple practice has caused one of the most deadly diseases known to man to become one of the most easily controlled. [Sidenote: Prevention of smallpox by vaccination:] Though it is well known that before the discovery of vaccination smallpox was a fatal disease, there are still some persons who say that vaccination has done nothing to reduce the mortality. When you learn some of the facts, you can judge for yourself whether or not vaccination does prevent smallpox. [Sidenote: (_1_) In the Franco-Prussian War]