Having succeeded, I trust, in proving to the entire satisfaction of every candid enquirer the possibility, if not the frequency, of the occurrence of Small Pox a second time in the same individual, it would be both interesting and useful, were it possible to ascertain what proportion such cases bear to those who escape a second attack; but many insurmountable difficulties present themselves in making such a calculation. Dr. Thomson tells us (p. 67), that “according to Tissot, the proportion of cases of secondary Small Pox, is as 1 in 100; according to Heberden, as 1 in 5000; and, according to Condamine, as 1 in 10,000. How uncertain the data!”—It is, however, enough to know, that while the relative number is sufficiently great to prevent the rule, That no individual can be affected by Small Pox oftener than once,—from being considered absolute, it is yet too small reasonably to shake our confidence in the fact, that a very large proportion will escape a recurrence of that disease. One other fact of considerable importance has, I trust, been also established by the preceding enquiry—That when secondary Small Pox does take place, it is usually a very mild disease, unattended with danger. The fourth argument in support of the employment of inoculation for Small Pox,—that it was rendered comparatively mild and devoid of danger, while it afforded equal security against any future attack of the disease with natural Small Pox itself, need not detain us long.—The latter part of the proposition has been generally admitted; and its truth or falsity will not affect the object of our present enquiry. Mr. Moore (History of Small Pox, p. 302) tells us, that “at the commencement of inoculation in England, the proportion of fatal cases appears to have been fully one in fifty. But after the last improvement in treatment had been established, probably not more than one in two hundred were lost.”—Mr. Moore continues—“of those who contract the casual Small Pox, and are treated with medical care, it has been admitted that generally about one in six are lost: but in countries where the medical arts are unknown, the Small Pox is so fatal a disease that few of those who are seized with it survive its malignity.” The immense difference between these proportions is amply sufficient to prove the great advantage derived from inoculation by those on whom it was practised.