That the doctrine of contagion is of comparatively modern origin (subsequently to Hippocrates), historical research fully shows, and it would be really an endless, if not an unprofitable, task to review the innumerable arguments of which contagionists and their opponents have from time to time availed themselves in support of their respective opinions, especially when the controversialists can enlist on the one side such names as Chisholm, Clark, Cleghorn, Pringle, Bianchi, Lind, Meade, Warren, and a host of others, as contagionists, and on the other side, as non-contagionists, such men as Hillary, Huck, Hunter, Jackson, Bouland, Pinckard, Bancroft, Scott, Rush, Miller, Caldwell, Chervin, besides very many others of more modern date. With reference to our present subject, contagion, it has always been with me a difficulty to understand the precise or real sense in which contagionists generally write; and I must confess my inability to comprehend the meaning they attach to the term contagion, and also to that of infection, so contradictory are their applications of the terms _contagion_ and _infection_, some using them synonymously, others making distinctions, between contagion and infection, of such arbitrary signification, that they are really neither definite nor intelligible; whilst contagionists themselves often depart from their _avowed_ principles. For example, Papôn, in his work entitled ‘Epoques Mémorables de la Peste,’ considers the undoubted causes of plague to be uncultivated lands, marshy soil, corrupt lakes, filthy cities, concurring with occasional causes, such as intemperature of the seasons and famine, whilst the bent of his researches is evidently to prove that in every modern plague _foreign_ contagion was the cause! Dr. Meade, notwithstanding his advocacy of contagion, like most other contagionists, is guilty of inconsistency in stating, “that a corrupt state of the air attends all plagues.” Again, Dr. Patrick Russell, a great contagionist, when giving a most minute account of the origin, spread, and decline of the plague, admits the inutility of quarantine laws for the prevention of contagion, and, curiously enough, he lays much stress on what he terms “a pestilential constitution of the air.” Dr. Hamilton, another great contagionist, affirmed that the influenza which prevailed in England,--in fact, all over Europe, in the year 1782, was contagious, and that the malady was propagated by contagion only; yet at the same time he informs us that, “in different places, many hundreds were seized with pestilence at one and the same time:” and Dr. (afterwards Sir Gilbert) Blane, also a contagionist, speaks of the influenza as having affected mariners in the very midst of the ocean!