Atmospheric air is a mixture, or compound, according to some, of two gases, oxygen and azote, with carbonic acid; but the proportion of the latter rarely exceeds two per cent, while the quantity of oxygen is about twenty-two. It is a solvent, as well as a vehicle, and hence may contain water, gaseous fluids, &c. Miasmata, which is contained often in the air, are vapours or effluvia, that affect the human system, and bring on diseases, of which the principal are the intermittent, remittent, and yellow fevers, dysentery and typhus. That of the last is generated in the human body itself. The same, or analogous causes, that produce the formation of nitric acid, may, under other circumstances, cause the formation of miasmata; for moist vegetable and other matter, in some unknown state of decomposition, generates it, and is known to have caused the yellow and other malignant fevers. (See an admirable work on the _causes, &c. of the yellow fever in Philadelphia_, by SAMUEL JACKSON, M. D. president of the board of health, etc. in reply to the observations of Dr. Hosack.) The contagious _virus_ of the plague, small pox, etc. as it operates in a more limited distance than marsh, or other miasmata, is communicated only in certain localities, and through the intermedium of the atmosphere. As to the chemical nature of miasmata, there can be no doubt that azote, under some form of combination, is one of its component parts, and one of the causes of disease. Is not cyanogen, or carburet of azote, perhaps combined with hydrogen, in the form of hydrocyanic or prussic acid, the substance, or _principal_ substance, which forms the miasmata, that engenders the yellow fever? What compounds may be formed of hydrogen, sulphur, phosphorus, carbon, and _azote_, so as to produce miasmata, that will act specifically on the system for the production of intermittent, remittent, yellow, typhus, and other fevers?[14] This inquiry, permit me to add, is one of no small moment, as it involves in it a question of great importance relative to the origin of yellow fever. While we thus digress, in noticing the compounds of azote, let us briefly remark, as an indisputable conclusion, that the same causes of malignant disease in the West India islands, operating under similar circumstances in every respect, may engender the same disease in our cities.