had mounted an engine and driven a host of confiding passengers to their destruction. This is the way in which he expressed himself, and it would be difficult to show that he was not correct. Intent on the discovery of some new anæsthetic, which might be more safely entrusted to general use, Dr. Snow began, in 1856, to experiment with amylene. As usual, he went to work cautiously and with precision. First he ascertained the boiling point of the specimen supplied to him; then the point of saturation of air with the vapour at different temperatures; then the effects of inhalation of the vapour by inferior animals, and the quantity required to be inspired, with the air breathed, to produce insensibility. These were the usual steps in all his inquiries of this kind. When he had obtained any substance which would produce insensibility favourably on animals, he pushed it, in one or two experiments, to its extreme in animals of different kinds; and having produced death by the inhalation, both by giving rapidly a large dose, and by giving a small dose for a long period, he observed the mode of death, whether it occurred by cessation of the heart, or by cessation of the respiration primarily. If the agent seemed to promise favourably from these inquiries, he commenced to try it on man; and the first man was invariably his own self. His friends, knowing his unflinching courage in the ardour of his inquiries, often expostulated with him in regard to the risks he ran. It was of no avail. He felt the personal trial a duty, and he did it. I do not believe, as some have supposed, that these personal experiments had any effect in producing his early death; but it is certain that he underwent many risks in the performance of his investigations, and that he held his own life of least consideration when the lives or well-being of others were under consideration. There is yet another trait in his character which I cannot but notice, and which I would respectfully commend to all physiological inquirers. While he held it as a necessity to use inferior animals for the purpose of experiment, he never touched living thing with the physiologist’s finger without having before him some definite object; and never performed experiment on any animal without providing with scrupulous care against the infliction of all unnecessary suffering. The interests of humanity were, according to his rule, best advanced by the practice of a humanity that was universal.