Medicine extends not so far. The remains of animals make us indeed acquainted, even now, with diseases to which the brute creation was subject long ere the waters overflowed, and the mountains sunk; but the investigation which is our more immediate object, scarcely reaches to the beginning of human culture. Records of remote and of proximate eras, lie before us in rich abundance. They speak of the deviations and destructions of human life, of exterminated and newly-formed nations; they lay before us stupendous facts, which we are called upon to recognise and expound in order to solve this exalted problem. If physicians cannot boast of having unrolled these records with the avidity of true explorers of Nature, they may find some excuse in the nature of the inquiry—for the characters are dead, and the spirits of which they are the magic symbols, manifest themselves only to him who knows how to adjure them. Epidemics leave no corporeal traces; whence their history is perhaps more intellectual than the science of the Geologist, who, on his side, possesses the advantage of treating on subjects which strike the senses, and are therefore more attractive,—such as the impressions of plants no longer extant, and the skeletons of lost races of animals. This, however, does not entirely exculpate us from the charge of neglecting our science, in a quarter where the most important facts are to be unveiled. It is high time to make up for what has been left unaccomplished, if we would not remain idle and mean-spirited in the rear of other naturalists. I was animated by these and similar reflections, and excited too by passing events, when I undertook to write the history of the “Black Death.” With some anxiety, I sent this book into the world, for it was scarcely to be expected that it would be everywhere received with indulgence, since it belonged to an hitherto unknown department of historical research, the utility of which might not be obvious in our practical times. Yet I soon received encouragement, not only from learned friends, but also from other men of distinguished merit, on whose judgment I placed great reliance; and thus I was led to hope that it was not in vain, and without some advantage to science, that I had unveiled the dismal picture of a long departed age.