which may be added Forts Gratiot, Crawford, and Wood--are so located as to be exposed to the prevalence of unusually severe winds or atmospheric currents either from the north-east or the north-west and west, with certain relations either to high mountain-ranges or ocean-currents. For instance, from Madison Barracks the open valley of the St. Lawrence River extends in a north-easterly direction to the Atlantic Ocean, where the cold ocean-current is from the north, favoring the pressure of cold atmospheric currents directly up the valley from the north-east, reaching its termination at the eastern end of Lake Ontario with but little diminution of force. The mountains of Northern New York, Vermont, and New Hampshire seem to prevent the deflection of these currents to the south, and help to keep them directly in the line of the valley. That the high ratio of attacks of bronchial and catarrhal affections at Madison Barracks is largely due to the influences here described is corroborated by the fact that the same class of diseases are much more prevalent in the province of Quebec, through which the valley of the St. Lawrence extends, than in the province of Ontario, as shown by the Registrar-General's Report in reference to the several {168} military posts in the Canadas. Turning to Forts Snelling and Crawford at the north and Jessup at the south, we find them so situated in relation to the great mountain-chains to the west as to be fully exposed to the cold and strong atmospheric currents that sweep over the Plains from the north-west and west with such force as to justify the popular title of blizzards. Without consuming more time in details, it may be said that the force and direction of atmospheric currents have quite as much to do with the development of inflammations of the air-passages, including all grades of bronchitis, as either temperature or humidity. As might be inferred from what has already been said in relation to the influence of climatic conditions, season of the year is also found to exert a marked influence over the prevalence of bronchial affections. Those parts of the year characterized by a low temperature, high winds, and frequent thermometric changes are accompanied by the highest ratio of prevalence of inflammations of the respiratory passages. Thus, the statistics compiled from the records of all the military posts by Drake show an average ratio for the four quarters of the calendar year of 119.8 for the first quarter, 72.7 for the second, 48.7 for the third, and 99.6 for the fourth.[4] This corresponds closely with the results of clinical records kept under my own observation through a series of years. [Footnote 4: See Drake on the _Principal Diseases of the Interior Valley of North America_, p. 792.]