Sir James Clarke says,--"It may be fairly questioned whether the proportion of cures of confirmed consumption is greater at the present day than in the time of Hippocrates: and although the public may continue to be the dupes of boasting charlatans, I am persuaded that no essential progress has been made or _can be made_ in the cure of consumption, until the disease has been treated upon different principles from what it hitherto has been. If the labor and ingenuity which have been misapplied in fruitless efforts to cure an irremediable condition of the lungs had been rightly directed to the investigation of the causes and nature of tuberculous disease, the subject of our inquiry would have been regarded in a very different light from that in which it is at the present period." While I shall not attempt a discussion of all the causes of _phthisis pulmonalis_, I shall, in a brief and familiar way, consider the more obvious sources of this terrible malady, and particularly those which all classes may remove or avoid. _Impure Air a Cause of Consumption._--In discussing the causes of a disease whose principal expression is in the lungs, nothing can be more legitimate than a consideration of the air we breathe. In full respiration, it penetrates every one of the many millions of air-cells. _Dust._--Every species of dust must prove injurious. Workers in those factories where tools are ground and polished soon die of pulmonary disease. The dust of cotton and woollen factories, that of the street, and that which is constantly rising from our carpets, are all mischievous. M. Benoiston found among cotton-spinners the annual mortality from consumption to be 18 in a thousand; among coal-men, 41; among those breathing an atmosphere charged with mineral dust, 30, and with dust from animal matter, as hair, wool, bristles, feathers, 54 per thousand: of these last the greatest mortality was among workers in feathers; least among workers in wool. The average liability to consumption among persons breathing the kinds of dust named was 24 per thousand, or 2.40 per cent. In a community where many flints were made, there was great mortality from consumption, the average length of life being only 19 years. _Gases._--Among the poisonous gases which infest our atmosphere, carbonic acid deserves special consideration. The principal result of all respiration and combustion, it exists in minute quantities everywhere, but when it accumulates to the extent of one or two per cent, it seriously compromises health. I have seen the last half of an eloquent sermon entirely lost upon the congregation; carbonic acid had so accumulated that it operated like a moderate dose of opium. No peroration would arouse them. Nothing but open windows could start life's currents. In lectures before lyceums, I often have a quarrel with the managers about ventilation. There is, even among the more intelligent, a strange indifference to the subject.