The instances, true or false, of a return are given out as having happened after a severe, as well as after a slight, small-pox. If a single pustule is no security, why should two, or a hundred? Or how many will be requisite? Were the probability of being safe from catching the small-pox again proportioned to the quantity of the eruption, inoculation, together with the rules given for the management of it, would be highly absurd; since both the rules and the practice, being intended to lessen the crop, would thereby tend to lessen the probability of never having it again.
A more palpable argument of this truth may be drawn from the very nature and course of the disorder. The inoculated small-pox is the ultimate effect of the variolous particle, which was applied to the skin. Now he, who has one pustule, undergoes an application to his skin of all the matter contained in the pustule; he is, in effect, inoculated on the spot, where the pustule is, and that much more powerfully than by the bare insertion of the atom of matter. The contents of this pustule being derived from the patient's own body, are more intimately united to it, in greater quantity, and for a longer time, than the particle inserted by inoculation, therefore a subject, after having once undergone the action of the variolous atom, was still liable to a fresh infection, his own pustule would inoculate him; this second infection would bring forth a third; and this a fourth; and so on, till he had exhausted the whole stock, or fell a victim to such a load of infection.