[49] As far as the Number of inoculated Persons, who remained entirely uninfected (some very few after a second Inoculation) has enabled me, I have calculated the Proportion naturally exempted from this Disease, though residing within the Influence of it, to be full 25 in 1000. See Analysis of Inoculation, Ed. 2d. P. 157. Note *. _K._ [50] It has sometimes been observed (and the Observation has been such, as not to be doubted) that a very mild distinct Small-Pocks has sometimes invaded the same Person twice: But such Instances are so very rare, that we may very generally affirm, those who have once had it, will never have it again. _E. L._----In Deference to a few particular Authorities, I have also supposed such a repeated Infection. (Analysis of Inoculation, Ed. 2d. P. 43.) though I have really never seen any such myself; nor ever heard more than two Physicians affirm it, one at _Versailles_, and another in _London_; the last of whom declared, he took it upon the Credit of a Country Physician, thoroughly acquainted with this Disease, and a Witness to the Repetition of it. Hence we imagine the Editor of this Work at _Lyons_ might have justly termed this Re-infection _extremely_ rare, which would have a Tendency to reconcile the Subjects of the Small-Pocks, more generally, to the most salutary Practice of Inoculation. Doubtless some other eruptive Fevers, particularly, the Chicken Pocks, Crystals, _&c._ have been often mistaken for the real Small-Pocks by incompetent Judges, and sometimes even by Persons better qualified, yet who were less attentive to the Symptoms and Progress of the former. But whoever will be at the Pains to read Dr. _Paux' Parallele de la petite verole naturalle avec l'artificielle_, or a practical Abstract of Part of it in the Monthly Review. Vol. XXV. P. 307 to 311, will find such a just, clear and useful Distinction of them, as may prevent many future Deceptions on this frequently interesting Subject. _K._ Sec. 203. People generally take the Small-Pocks in their Infancy, or in their Childhood. It is very seldom known to attack only one Person in one Place: its Invasions being very generally epidemical, and seizing a large Proportion of those who have not suffered it. It commonly ceases at the End of some Weeks, or of some Months, and rarely ever appears again in the same Place, until four, five or six Years after.