It is not, however, my intention to enter into any detail of the mode in which Vaccination originated, or of the circumstances which accompanied its introduction into practice. It will suffice to state, that its supposed efficacy in preventing the occurrence of Small Pox, was founded upon repeated observation, that the milkers employed in the great dairies of Gloucestershire and the neighbouring counties, who became affected with a disease which prevailed among the cows, and to which the name of Cow Pox had been given in consequence, were very generally rendered insusceptible of the Small Pox infection, even when attempted to be communicated by means of inoculation. Dr. Jenner put this fact to the test of repeated experiment, and finding it thus confirmed, proposed introducing the Cow Pox into the human constitution artificially, as a means of securing it against the dangers of Small Pox, and, in the end, of entirely exterminating the latter disease; for it must appear very evident, that if every individual could in any way be rendered incapable of being infected by Small Pox, the infection itself must necessarily become entirely extinct. In prosecuting my enquiries into this part of my subject I shall, as far as may be, confine myself to an examination of facts calculated, as I conceive, to remove every reasonable doubt respecting the true value of Vaccination. The first essential fact, to which I would direct the attention of my readers, is the very striking diminution in the number of deaths from Small Pox, which has taken place within the bills of mortality of London, since the introduction of Vaccination. This diminution is equally remarkable, whether we refer to the actual number of deaths from this cause, or to the relative proportion which they bear to the whole amount of deaths occurring in any given year or number of years. Thus taking the averages calculated on periods of five years each, as is shewn in the table (No. 2), it will appear evident not only that the amount of diminution has been most gratifying and satisfactory, but that, in proportion to the increasing employment of Vaccination, it has been regularly progressive; so that the number of deaths from Small Pox, instead of amounting to one in ten of the whole, as was the case for the ten years which preceded the introduction of Vaccination, has during the last ten years, actually amounted to less than one in twenty-eight, or little more than one-third of the former proportion.