Dr. Hart said that thirty years ago, in a country region of western Pennsylvania, he met an epidemic of smallpox. Over thirty years earlier, under a State law, the whole community had been vaccinated. Out of about fifty persons exposed to the disease the most were adults who had been vaccinated at the time referred to, or earlier. Referring to an article on the epidemic prepared at the time, he finds that fully half had the disease in some form, from the mildest varioloid to confluent smallpox, one case of secondary smallpox occurring. While he believed that fifty per cent. of those vaccinated in infancy are protected for a lifetime, still he regards the presence of the most distinct cicatrix as no criterion by which to determine who are thus secure. From twelve to twenty years of age, probably, fully one-half will have a more or less perfect result from revaccination, and will in most cases be thenceforth protected from all ordinary exposure to smallpox. But in the presence of the varilous atmosphere of an epidemic of the disease, revaccination is the only absolute safety. He has always revaccinated himself as often as exposed, and advised the same course for others. While smallpox prevailed here, say from 1865 to 1873, where patients were not removed to a pest house, and the only precaution enforced was the notice on the house, he attended a considerable number of cases. He always insisted on vaccinating every exposed person, and although there were often unvaccinated children and adults who had a thorough effect from revaccination, he never had a second crop of calls in the same house. He referred to the complete revaccination of the Forty-first Regiment, O. V. I., before going South. Many of the men with a fair cicatrix had a perfect revaccination, while two hundred or three hundred had more or less result. Humanized virus was used. During their term of service, while repeatedly exposed to smallpox, and where other regiments about them suffered severely from the disease, they entirely escaped. This immunity could only be referred to their revaccination, and certainly affords the strongest proof of its prophylactic power. While frequent renewals of the humanized virus is desirable, he regarded it, when selected with the care which ought to be observed, as milder in its effects and much more certain than cowpox. In vaccinating with cowpox he has had severe effects follow much more frequently than when he made use of the humanized virus. Dr. Dutton did not believe that the profession should insist on compulsory revaccination, at least until it was proven that revaccination was absolutely necessary. A second vaccination often produces a serious inflammatory sore, quite unlike the true vaccine pustule, and an ulcer sometimes follows. Dr. Preston stated that, as he had observed, a large percentage of those who were not revaccinated were liable to have varioloid.