vestigations as to the geological formations and
fossils found in his neighborhood.

Even during his student days with Hunter he had been much interested in
the belief, current in the rural districts of Gloucestershire, of the
antagonism between cow-pox and small-pox, a person having suffered
from cow-pox being immuned to small-pox. At various times Jenner had
mentioned the subject to Hunter, and he was constantly making inquiries
of his fellow-practitioners as to their observations and opinions on the
subject. Hunter was too fully engrossed in other pursuits to give the
matter much serious attention, however, and Jenner's brothers of the
profession gave scant credence to the rumors, although such rumors were
common enough.

At this time the practice of inoculation for preventing small-pox, or
rather averting the severer forms of the disease, was widely practised.
It was customary, when there was a mild case of the disease, to take
some of the virus from the patient and inoculate persons who had never
had the disease, producing a similar attack in them. Unfortunately there
were many objections to this practice. The inoculated patient frequently
developed a virulent form of the disease and died; or if he recovered,
even after a mild attack, he was likely to be "pitted" and disfigured.
But, perhaps worst of all, a patient so inoculated became the source of
infection to others, and it sometimes happened that disastrous epidemics
were thus brought about. The case was a most perplexing one, for the
awful scourge of small-pox hung perpetually over the head of every
person who had not already suffered and recovered from it. The practice
of inoculation was introduced into England by Lady Mary Wortley Montague
(1690-1762), who had seen it practised in the East, and who announced
her intention of "introducing it into England in spite of the doctors."

From the fact that certain persons, usually milkmaids, who had suffered
from cow-pox seemed to be immuned to small-pox, it would seem a very
simple process of deduction to discover that cow-pox inoculation was the
solution of the problem of preventing the disease. But there was another
form of disease which, while closely resembling cow-pox and quite
generally confounded with it, did not produce immunity. The confusion of
these two forms of the disease had constantly misled investigations as
to the possibility of either of them immunizing against smallpox, and
the confusion of the