oes not this
give an idea, that if they were both inoculated at the same time, that
neither of them might affect the patient?

From these cases I contend, that the contagious matter of these diseases
does not affect the constitution by a fermentation, or chemical change of
the blood, because then they must have proceeded together, and have
produced a third something, not exactly similar to either of them: but that
they produce new motions of the cutaneous terminations of the
blood-vessels, which for a time proceed daily with increasing activity,
like some paroxysms of fever, till they at length secrete or form a similar
poison by these unnatural actions.

Now as in the measles one kind of unnatural motion takes place, and in the
small-pox another kind, it is easy to conceive, that these different kinds
of morbid motions cannot exist together; and therefore, that that which has
first begun will continue till the system becomes habituated to the
stimulus which occasions it, and has ceased to be thrown into action by it;
and then the other kind of stimulus will in its turn produce fever, and new
kinds of motions peculiar to itself.

10. On further considering the action of contagious matter, since the
former part of this work was sent to the press; where I have asserted, in
Sect. XXII. 3. 3. that it is probable, that the variolous matter is
diffused through the blood; I prevailed on my friend Mr. Power, surgeon at
Bosworth in Leicestershire to try, whether the small-pox could be
inoculated by using the blood of a variolous patient instead of the matter
from the pustules; as I thought such an experiment might throw some light
at least on this interesting subject. The following is an extract from his
letter:--

"March 11, 1793. I inoculated two children, who had not had the small-pox,
with blood; which was taken from a patient on the second day after the
eruption commenced, and before it was completed. And at the same time I
inoculated myself with blood from the same person, in order to compare the
appearances, which might arise in a person liable to receive the infection,
and in one not liable to receive it. On the same day I inoculated four
other children liable to receive the infection with blood taken from
another person on the fourth day after the commencement of the eruption.
The patients from whom the blood was taken had the disease mildly, but had
the most pustules of any I could select from twenty inoculated pati