The next great advance was the discovery by Pasteur of the possibility of so attenuating, or weakening, the poison that an animal inoculated had a slight attack, recovered and was then protected against the disease. More than eighty years had passed since on May 14, 1796, Jenner had vaccinated a child with cowpox and proved that a slight attack of one disease protected the body from a disease of an allied nature. An occasion equally famous in the history of medicine was a day in 1881, when Pasteur determined that a flock of sheep vaccinated with the attenuated virus of anthrax remained well, when every one of the unvaccinated infected from the same material had died. Meanwhile, from Pasteur's researches on fermentation and spontaneous generation, a transformation had been initiated in the practice of surgery, which, it is not too much to say, has proved one of the greatest boons ever conferred upon humanity. It had long been recognized that, now and again, a wound healed without the formation of pus, that is, without suppuration, but both spontaneous and operative wounds were almost invariably associated with that process; and, moreover, they frequently became putrid, as it was then called,--infected, as we should say,--the general system became involved and the patient died of blood poisoning. So common was this, particularly in old, ill-equipped hospitals, that many surgeons feared to operate, and the general mortality in all surgical cases was very high. Believing that it was from outside that the germs came which caused the decomposition of wounds, just as from the atmosphere the sugar solution got the germs which caused the fermentation, a young surgeon in Glasgow, Joseph Lister, applied the principles of Pasteur's experiments to their treatment. From Lister's original paper(*) I quote the following: "Turning now to the question how the atmosphere produces decomposition of organic substances, we find that a flood of light has been thrown upon this most important subject by the philosophic researches of M. Pasteur, who has demonstrated by thoroughly convincing evidence that it is not to its oxygen or to any of its gaseous constituents that the air owes this property, but to minute particles suspended in it, which are the germs of various low forms of life, long since revealed by the microscope, and regarded as merely accidental concomitants of putrescence, but now shown by Pasteur to be its essential cause, resolving the complex organic compounds into substances of simpler chemical constitution, just as the yeast-plant converts sugar into alcohol and carbonic acid." From these beginnings modern surgery took its rise, and the whole subject of wound infection, not only in relation to surgical diseases, but to child-bed fever, forms now one of the most brilliant chapters in the history of preventive medicine. (*) Lancet, March 16, 1867. (Cf. Camac: Epoch-making Contributions, etc., 1909, p. 7.--Ed.)