The victims of the Black Hole in Calcutta and of the Steamer Londonderry, with the thousand other instances in which immediate death has resulted from carbonic acid, are terrible examples in the history of human suffering; but these cases are all as nothing, compared with those of the millions who nightly sleep in unventilated rooms, from which they escape with life, but not without serious injury. As a medical man, I have visited thousands of sick persons, and have not found one hundred of them in a pure atmosphere. I have often returned from church seriously doubting whether I had not committed a sin in exposing myself to its poisonous air. There are in our great cities churches costing fifty thousand dollars, in the construction of which not fifty dollars were expended in providing means for ventilation. Ten thousand dollars for ornament, but not ten dollars for pure air! Parlors with furnace-heat and a number of gas-burners (each of which consumes as much oxygen as several men) are made as close as possible, and a party of ladies and gentlemen spend half the night in them. In 1861 I visited a legislative hall. The legislature was in session. I remained half an hour in the most impure air I ever attempted to breathe. If the laws which emanated from such an atmosphere were good, it is a remarkable instance of the mental and moral rising above a depraved physical. Our school-houses are, some of them, so vile in this respect that I would prefer to have my son remain in utter ignorance of books, rather than breathe, during six hours of every day, so poisonous an atmosphere. Theatres and concert-rooms are so foul that only reckless people can continue to visit them. Twelve hours in a railway-car exhausts one, not because of the sitting, but because of the devitalized air. While crossing the ocean in the Cunard steamer Africa, and again in the Collins steamer Baltic, I was constantly amazed that men who knew enough to construct such noble ships did not know enough to furnish air to the passengers. The distresses of sea-sickness are greatly intensified by the sickening atmosphere which pervades the ship. Were carbonic acid black, what a contrast would be presented between the air of our hotels and their elaborate ornamentation! It is hardly necessary to say that every place I have mentioned might be cheaply and completely ventilated. Consumption originates in the tubercular diathesis. This diathesis is produced by those agencies which deprave the blood and waste vitality. Of these agencies none is so universal and potent as impure air. When we consider, that, besides mingling momentarily with the blood of the entire system, it is in direct and constant contact with every part of the lungs, we cannot fail to infer that foul air must play a most important part in that local expression of the tubercular taint known as pulmonary consumption. The author of an excellent work on consumption declares,--