changes upon it, until it has
acquired the contagious and malignant form under which we now
commonly see it making its devastations amongst us? And, from a
consideration of the change which the infectious matter undergoes
from producing a disease on the cow, may we not conceive that many
contagious diseases, now prevalent among us, may owe their present
appearance not to a simple, but to a compound origin? For example, is
it difficult to imagine that the measles, the scarlet fever, and the
ulcerous sore throat with a spotted skin, have all sprung from the
same source, assuming some variety in their forms according to the
nature of their new combinations? The same question will apply
respecting the origin of many other contagious diseases, which bear a
strong analogy to each other.

There are certainly more forms than one, without considering the
common variation between the confluent and distinct, in which the
Small-pox appears in what is called the natural way.--About seven
years ago a species of Small-pox spread through many of the towns and
villages of this part of Gloucestershire: it was of so mild a nature,
that a fatal instance was scarcely ever heard of, and consequently so
little dreaded by the lower orders of the community, that they
scrupled not to hold the same intercourse with each other as if no
infectious disease had been present among them. I never saw nor heard
of an instance of its being confluent. The most accurate manner,
perhaps, in which I can convey an idea of it is, by saying, that had
fifty individuals been taken promiscuously and infected by exposure
to this contagion, they would have had as mild and light a disease as
if they had been inoculated with variolous matter in the usual way.
The harmless manner in which it shewed itself could not arise from
any peculiarity either in the season or the weather, for I watched
its progress upwards of a year without perceiving any variation in
its general appearance. I consider it then as a _variety_ of the
Small-pox[3].

In some of the preceding cases I have noticed the attention that was
paid to the state of the variolous matter previous to the experiment
of inserting it into the arms of those who had gone through the
Cow-pox. This I conceived to be of great importance in conducting
these experiments, and were it always properly attended to by those
who inoculate for the Small-pox, it might prevent much subsequent
mischief and confusion. With the vie