CHAPTER III. HISTORICAL SKETCH. In the Old Testament, frequent allusion is made to contagion, particularly in Leviticus, where directions are given for the expurgation, from the system, of that principle; for the isolation of persons possessed of it; and the cleansing of garments therewith infected. The earliest Grecian historians make reference to it, and Thucydides, in his History of the Plague, attributes some occurrences in its career, to the operation of that principle. Dr Winterbottom[1] writes thus, of an ancient physician—“Aratæus says, that the miserable patients (those ill of Elephantiasis), were banished into deserts, or to the top of mountains, where the kindness of their friends occasionally attended their distresses; though perhaps they were more frequently deserted.” Footnote 1: Dr Winterbottom on Sierra Leone. Cælius Aurelianus, a noted physician, says—“Some advise that a person labouring under this disease, should be turned out of town, if a stranger, or if an inhabitant, be banished to some distant part; others advise the patient to be totally abandoned.” These expressions relate to contagion generally. Atmospheric contagion is not specified, though perhaps even then, it may have been thought to exist. As already said, later physicians thought that contagious diseases were propagated in three different ways, _1st_, by actual contact with the matter or virus itself; _2dly_, by fomites, or by contact with clothes tainted with it; and, _3dly_, by infection, or by air holding it in solution. But it is to contagion, as diffused through the air, that the observations that are to follow are directed. So we shall, for the present at least, dismiss the other two modes of its action, that by contact, and that by fomites or tainted clothes, with the expression of our belief in their existence, as modes of the propagation of disease. In 1777, Dr Haygarth, an English physician, began to investigate the laws that regulate the action of contagious poisons, and for the first time they obtained a scientific examination, and became the subject of experiment, if, perhaps, are excepted the labours of Lind, whose observations appeared about the same time. Dr Haygarth believed in the propagation of disease through the direct application of contagious matter, such, for instance, as that of small-pox; but of this none have expressed any doubt worthy of notice; for the fact is well known, and often witnessed, by inoculation for small-pox and cow-pox. At the time at which Dr Haygarth wrote, very vague and extravagant notions were held on the subject of contagious poisons diffused in the air—of air holding in solution contagious poison, or, as we have determined to call it—Atmospheric Contagion. It was believed to extend itself to great distances, and there to develope its powers.