It is now twenty-one years since Vaccination was promulgated in this country by Dr. Jenner, and fifteen years since it began to produce a sensible effect in diminishing the mortality from Small Pox. In regard to the latter period, it is coeval with this Society; yet, though no discovery in nature nor in medicine has been more important to the interests of humanity, nor any which has ever so rapidly and universally won the assent and practical adoption of mankind, there are no notices of it on our records, except in our second volume, in an article by Dr. Bateman, in which he relates a case of a mother who was affected with the Small Pox a second time, by being exposed to infection, from some of her own children who had caught it casually; while her other children, who had been vaccinated, resisted it. As it is to be hoped that our labours will prove to posterity some of the principal sources of reference regarding the medical and chirurgical discoveries and improvements of the age; as it is one of the reproaches of our country, that it has not availed itself so much as any other of the benefits of Vaccination; and as there are writers among us who still allege that the failures are so numerous that the value of the discovery is very ambiguous, it seems one of the duties of the Society to lend its aid in placing these important points in their true light. It seems almost needless to premise, that the Small Pox is of all maladies that, which, during the last thousand years, has destroyed the largest portion of the human species, and been productive of the largest share of human misery. There is, perhaps, no disease over which medical art has less power; and this power, such as it is, has consisted more in abolishing pernicious practices, than in ascertaining any positive methods of controlling its fatality, unless we except the inoculation of it with its own _virus_. But, though the beneficial effect of this on those on whom it is actually practised is undeniable, it has no tendency like Vaccination to extirpate the disease; and from the impossibility of rendering it universal, it has actually been found to add to the general mortality of Small Pox, by opening a new source for the diffusion of its _virus_. It ought to be stated also, with a view to a decision on this question, that Vaccination itself is attended with no danger, and frequently takes effect without any visible disturbance in the system. There is even reason to believe, that in its process it wards off other diseases, by pre-occupying the constitution.