As I can from considerable experience speak with some confidence on this subject, I shall proceed to relate the observations that have occurred to me. Assisted by my learned friend Dr. Ingenhouz and my two sons, I inoculated, at different times, the neighbouring parishes of East Berkhamsted, Hertingfordbury, Bayford, and the liberty of Brickenden; in each of these places the whole number of poor were inoculated, with the exception of those who were objectionable. I do not at present remember the exact number, I believe they might be more than 600; but know that they succeeded happily, though there were several very old persons, and women in different periods of gestation; and this mode of practice, as I have been informed, has been also used successfully by many others in different parts of England. So far as has come to my knowledge, general Inoculations have hitherto been confined to small towns and villages; yet as the further extension is very much to be wished, it may not be improper to relate some particulars of what passed in Hertford, which is doubtless the largest, and most populous town, that has submitted to the experiment of inoculating at the same time the whole number of its inhabitants. In a former publication, I gave an account of the occasion and success of a general Inoculation at this place; from that time the town was released from any apprehensions of the disease, until the year 1770, when it appeared again, and two or three having died, a few persons were inoculated, and excited an alarm. On this occasion, the poor in my neighbourhood flocked in numbers, beseeching me to extend to them the same charitable assistance, they had formerly experienced; having then my two sons with me to assist, I complied without hesitation. Nothing shews the increase and state of population so clearly, as an experiment of this kind; we had then upwards of two hundred and fifty patients, some of whom were new inhabitants, but the rest consisted for the most part of very young children. Necessity has often produced useful discoveries; the Inoculation was begun on Midsummer-day, and though the weather proved very hot, I observed no inconvenience from it; they had the free use of air, and seemed as much benefited by it as at any other season of the year; and every one recovered. In the year 1774 the disease appeared a third time; the same request was renewed, and with the same assistance afforded, the whole town was inoculated once more, and now the number amounted only to about one hundred and twenty; from that time we have heard nothing of Small Pox, and I verily believe, that within these ten years not six persons have died in Hertford of this disease; whereas before the practice was so generally adopted, the Small Pox has frequently been epidemic and destroyed a great number of the inhabitants, besides injuring the market and trade of the town for a considerable time.