After the plague of the Antonines we come to the great plague of Justinian and here at last we have the evidence of an exact historian who did not run and could state what he saw in language that we can understand. Gibbon says hesitantly that Procopius was a doctor, though probably in truth he was a lawyer. Possibly he was too much afraid of the naughty little Empress Theodora, whom he was afterwards to slander, to forsake the path of duty and run away when the world seemed dying; but at any rate he has left us a remarkable account of the plague of 542, one of the most terrible recorded visitations of epidemic disease; and after reading Gibbon’s somewhat excitable account of it I think that few doctors will deny that it was real old bubonic plague that has so often made history. Justinian suffered from it and recovered; we do not know enough about the exact circumstances to estimate its exact effects upon the world; but we can be pretty certain that the bacillus pestis did not lay waste the Byzantine Empire for nothing. Gibbon estimates the total loss of life at a hundred millions; but one doubts if the population of the Roman Empire, even in its palmiest days, was ever much larger, and surely the plague could not have swept off everybody in the known world, though we do know that, if it really breaks loose in flea-bitten surroundings, plague can do an infinity of mischief, probably more than any other known disease. We leave the dead old world that shook at Cæsar’s nod, and leap in one moment to the very beginnings of the modern world, to the Black Death of 1348; for, though the Middle Ages were still to drag their slow length along for at least a century, there can be little doubt that after the Black Death had terrified mankind all our modern problems were beginning, if only in embryo. The original source of it seems to have been China, and the epidemic proceeded with most leisurely footsteps until it took ship for Europe. Dr. Hecker[20] in 1833 wrote an exhaustive account of it from mediæval records; but since 1833 the cell-theory of Schleiden and Schwann has revolutionised medicine, and even Dr. Hecker has to be translated into modern terminology; so rapidly has medicine changed that a book written ten years ago is already obsolete. Indeed, it is not too much to say that more has been discovered in medicine within the last thirty years than in the whole previous half-million years during which man has been upon the earth; one sometimes becomes terrified at the amazing growth of knowledge. Whither is it all leading us? Are we becoming as gods? Vespasian joked about himself when he was dying; let us not really grow “pumpkinified,” to use Seneca’s words about Claudius, when we think ourselves becoming deified.