The predisposing causes are as numerous as the varied influences which operate to depress the general health. The insalubrity of the atmosphere may be regarded as a general, and, perhaps, the most extensive predisposing cause. In this state, its vital element becomes diminished or impaired to such an extent as to render it incapable of sustaining the normal and healthy functions of the system in their most vigorous condition. Hence, the foul and noisome air of close, ill-ventilated apartments becomes very depressing and baneful; a direct and effective element, often, in constant operation in generating and producing the cholera, typhoid fever, or other deadly maladies. This is not unfrequently the case on board some of our emigrant ships, when hundreds of human beings are stowed away between decks without the means of efficient ventilation, disinfection, or other mode of expelling the noxious principle. Though the germ of disease may be ever on board, it does not vegetate and come forth and rapidly acquire its activity, vigor and power, unless the localizing influence vivify, foster and nurture its development. This is fully confirmed by the recent arrival of two steamers with cholera on board. The _England_, and a few days later the _Virginia_, with crews and passengers all in perfect health, departing from a healthy port where no cases of cholera were known to exist, and after being out at sea six or eight days under the influence of a cool, invigorating atmosphere, were surprised by the sudden irruption of cholera on board. It breaks out among the steerage passengers who are crowded and packed together between decks like sheep for the slaughter, in a confined atmosphere, daily becoming more noisome, without the means of ventilation or disinfection. Can any sane man say the disease--the cholera--was not here, on board these ships, generated and produced? This is also confirmed by the occurrence of an isolated case on Ninety-third Street, near Third Avenue, the first case in this city this season. Though the cholera exists at Quarantine, the patient had not been in any way exposed to the disease, except to the exhalations from the overflowing and drainage of a privy and the foul atmosphere arising from the cellar of her own tenement. On Monday, it is said, she partook of her dinner, feeling a little indisposed; at 4 P.M. she called in her physician, and died the next morning, May 1st, at 11 A.M., in a state of collapse. Take another instance: the second case in this city occurred in one of the tenement dwellings of the Sixth Ward, No. 117 Mulberry Street. The patient was a woman about thirty years of age, who had not been exposed, except to the noisome atmosphere of her own dwelling and its surroundings, which must be regarded, under the peculiar circumstances, as a true, genuine cholera atmosphere. In these cases the evidence is conclusive that the disease was generated and produced within, and on these premises.