In their efforts to make out their case, there would seem to be no end to the contradictions and inconsistencies into which the advocates of contagion in cholera are led. At one moment we are required to believe that the disease may be transmitted through the medium of an unpurified letter, over seas and continents, to individuals residing in countries widely differing in climate, while, in the next, we are told--regarding the numberless instances of persons of all habits who remain unattacked though in close contact with the diseased--that the constitution of the atmosphere necessary for the germination of the contagion is not present; and this, although we see the disease attacking all indiscriminately, those who are not near the sick as well as those who are at a very short distance, as on the opposite side of a ravine, of a rivulet, of a barrack, or even of a road. They assume that wherever the disease appears, _three_ causes must be in operation--contagion--peculiar states of atmosphere (heat now clearly proved not _essential_, as at one time believed)--and susceptibility in the habit of the individual. However unphilosophical it is held to be to multiply causes, the advocates of contagion are not likely to reduce the number, as this would at once cramp them in their pleadings before a court where sophistry is not always quickly detected. Those who see irresistible motives for dismissing all idea of contagion, look, on the contrary, for the production of cholera, to sources, admitted from remote times to have a powerful influence on our systems, though invisible--though not to be detected by the ingenuity of man, and though proved to exist only by their effects.