A very few years ago it was the general opinion, even of the best informed, that epidemic diseases originate in atmospheric influences over which man has no control. A reservation seems, however, to have been made in respect of the Oriental, or as some term it, the African, plague, a malady the most frightful to which man is liable. Writers of the highest order traced to a damp, hot, and stagnating air, generated from the putrefaction of animal substances, and especially from the swarms of locusts, not less destructive to mankind in their death than in their lives, the fatal disease which depopulated the earth in the time of Justinian and his successors. The disease was reported to have first appeared in the neighbourhood of Pelusium, between the Serbonian bog and the eastern channel of the Nile. Thence tracing a double path it spread to the east, over Syria, Persia, and India, and penetrated to the west, along the coast of Africa, and thence to the continent of Europe. But in order to explain how it spread, it was necessary to invent another theory and add it to the first; the disease once generated, was said to spread by contagion. It is related in “The Decline and Fall of the Roman Empire,”[11] that in the spring of the second year (after its first appearance), Constantinople, during three or four months, was visited by the pestilence. It did not reach the capital of the empire at once, but travelled slowly and irregularly, after the manner of modern cholera. In the admirable descriptions of the immortal historian, we can trace all the symptoms of the true Oriental plague, identical in its phenomena and effects with the sufficiently numerous visitations which have since occurred, and with that no doubt which, lately originating at Bengazzi, and spreading to Tripoli, once more threatens the European family of nations. In a damp, hot, stagnating air, observes the historian, who in his account follows Procopius, this African fever is generated from the putrefaction of animal substances, and especially from the swarms of locusts, “not less destructive to mankind in their death than in their lives.” But the ferment and putrefaction thus created scarcely accounts for the origin of the disease, and its extension north-wards into the coldest regions of Europe is inexplicable on such a hypothesis, though aided by the modern hypothesis that its propagation is due simply to the neglect of sanitary regulations, a theory now happily extended to all zymotic diseases. Passing over the question as to the contagious nature of plague, typhus, cholera, scarlatina, measles, a question still undecided, and adhering simply to facts, we are assured by Procopius, the fidelity of whose descriptions the great historian seems disposed to vouch for, that the disease always spread “from the sea coast to the inland country; the most sequestered islands and mountains were successively visited; the places which had escaped the fury of its