conversation; for
should anything untoward turn up in my experiments I should be made,
particularly by my medical brethren, the subject of ridicule--for I am
the mark they all shoot at."

Jenner's reasons for concealment did not arise from any selfish or
unworthy motive. The publicity he had always given to the subject and
the efforts he had made among his professional associates to pursue the
inquiry exclude the possibility of entertaining such a suspicion. It
arose from a dread of disappointment and the fear of failure should the
matter be brought forward in a state other than that of a maturity
sufficient to carry conviction immediately upon its promulgation. In the
course of his researches he was led to conclude that swinepox, as well
as cowpox, was only a variety of smallpox. He inoculated his eldest son
with the matter of swinepox and produced a disease similar to a very
mild smallpox. After this, the inoculation of variolous matter would
produce no effect.

He ascertained that cowpox, as it was commonly termed by the milkers,
would frequently fail in effecting a security against the smallpox. This
led him to inquire more particularly into the variety of spontaneous
eruptions to which the teats of the cow were liable, and to discriminate
the different kinds of sores produced by them on the hands of the
milkers, and to establish the character of those which possessed a
specific power over the constitution, and those which had no such
efficacy. He found that instances occurred in which the true cowpox
failed in preventing smallpox; but nothing daunted by this apparently
fatal discovery he set about ascertaining the causes of this deviation.
He found the specific virtues of the virus to have been lost or
deteriorated so that it was rendered capable only of producing a local
affection and had no influence whatever upon the constitution; and by
the greatest ingenuity and patience of observation of the analogies
drawn from the virus of smallpox, aided by his knowledge of the laws of
the animal economy, he discovered that it was only in a certain state of
the vesicle that the virus was capable of affording its protecting
agency, and that when taken under other conditions, or at other periods,
it could produce a local disease, yet that it was not able to manifest
any constitutional effect, or afford immunity from the invasions of the
smallpox.

On May 14, 1796, Jenner inserted lymph taken from the hand of Sarah
Nelme