The subject is indeed so surprising that I prefer to quote the passage with regard to these experiments directly from Dr. Baron:
"In November, 1789, he inoculated his eldest son Edward, who was then about one year and a half old, with swine-pox matter. The progress of the disease seemed similar to that which arises from the insertion of true smallpox matter when the disease is very slight. He sickened on the eighth day: a few pustules appeared; they were late and slow in their progress, and small. Variolous matter (this would mean material from a smallpox patient calculated to give that disease) was carefully inserted into his arms at five or six different periods, subsequently without the slightest inflammation being excited in the part.
"On Thursday, April 7th, 1791, variolous matter was again inserted by two small incisions through the cutis, [beneath the skin]. Then the following notes of observed conditions day after day are made: 9th, Evidently inflamed. 10th, An efflorescence of the size of a shilling spread round the inferior wound. 11th, The incision assumed a kind of erysipelatous elevation: the efflorescence much increased. 12th, These appearances much advanced. 13th, A vesicle, containing a brownish fluid, and transparent, about the size of a large split-pea on the superior incision, the inferior about twice as big; the surrounding parts affected with erysipelas. The erysipelas extended to the shoulder, and then pretty quickly went off. The child showed no signs of indisposition the whole time."
"March, 1792. E. Jenner was again inoculated: the matter was taken from a child that caught the disease in the natural way, and had it pretty full. It was inserted fresh from the pustule. The same evening an inflammation appeared round the incision, which, at the end of twenty hours, increased to the diameter of a sixpence, and some fluid had already been collected on the lips of the scratch, which the child had rubbed off."
It was not for five years after this time, however, that Jenner was able to make his crucial experiments in the matter. On the 14th of May, 1796 (the date is still recalled as Vaccination Day in Germany, especially in Berlin), vaccine matter was taken from the hand of a dairy maid, Sarah Nelmes, and inserted by two superficial incisions in the arms of James Phipps, a healthy boy of about eight years of age. The boy went through an attack of cowpox in a regularly satisfactory manner. After this, however, it was necessary to determine whether he was protected from smallpox. After waiting two months Jenner inoculated him with variolous material. The result of this experiment can best be learned from the following letter written to his friend Gardner: