These are Jenner’s Cases. In them we have his “Masterpiece of Medical Induction”--the fruit of thirty years of incessant thought, of watching, and of experiment! Let us carefully observe the dates. Until 1796, when he operated on Phipps, he never made an experiment in Horsegrease Cowpox Inoculation; and not until the middle of March, 1798, a few weeks before going to press with the _Inquiry_, did he repeat the experiment; and though his later cases were complicated with erysipelas, he did not stay to dispose of the difficulty and alarm thereby excited. He got together his scratch lot of Cases, as if under some over-mastering compulsion, and consigned the concern, crude and incomplete, to the public. By-and-by the hasty performance came to be spoken of as the result of thirty years of incessant thought, of patient research, and of unwearied labour. It is unnecessary to argue the matter. Whilst there is nothing too great for the credulity of those who are in the disposition of belief, yet facts are facts, and there is the stone-wall of the _Inquiry_ with its authentic details whereon to crack the skulls of romancers. In Jenner’s story as recited to the vulgar, we have the advantage of witnessing the development of myth in the light of our own age under our own eyes. Taking Jenner’s _Inquiry_ at the utmost, What was it? A suggestion to substitute Horsegrease Cowpox for Smallpox in inoculation. That was all. Beyond this there was no point of novelty. Some have credited Jenner with originating the transfer of virus from arm to arm; but in this respect he followed the example of many variolators. There was a mild form of Smallpox occasionally prevalent in London called “pearly pox,” and Dr. Adams and others kept it going from patient to patient; and the virus from the body of a healthy variolated child was in constant request by timid folk, who fancied the virulence of the original infection might thereby be abated in transmission. So much for Jenner’s data. Now for a word or two as to the speculation that invested his prescription. He considered that some of the diseases which afflict men are derived from their domestication of animals, and that thus several diseases might have a common origin. “For example,” he asked, “Is it difficult to imagine that measles, scarlet fever, and ulcerous sore throat with a spotted skin, have all sprung from the same source?”