Page:Popular Science Monthly Volume 40.djvu/848

826 and purer air being heavier than the heated impure air, and therefore nearer the line of the floor.

Animals furnish the same evidence. Cows and horses both suffer grievously from want of ventilation in their stables; and cattle, though they require warmth for fattening, still put on flesh better in a colder but well-ventilated place than in a warmer place which is unventilated (Parkes, page 180). So also Parkes tells us about the French cavalry. Before 1836 the mortality among the horses varied from 180 to 197 per 1,000 per annum. With the enlargement of the stables and increased quantity of air, the loss was reduced to 68 per 1,000, and finally to 28 per 1,000, and of officers' horses to 20.

Then we have the evidence of the ordinary tests for ascertaining the purity of the air. Air fouled by respiration discolors permanganate of potash and robs it of a portion of its oxygen; the amount of organic matter is then measured by the number of volumes of oxygen required to reoxidize the permanganate and restore it to its former condition. Another test is the presence of certain bacteria, which are found in large numbers in foul air, increasing out of proportion to the molds or fungi found in the air, which appear to be much less affected by impurities. It is stated that these forms of life all originally come from the open air—that reservoir of all things—though they are supposed to multiply in congenial quarters when once they have found an entrance. The significant fact, however, is their number, which might seem to show that they prosper just because they have discovered their proper food—the organic poison which Is poured out into the air from our lungs and skin. On this point. Dr. A. Ransome makes an interesting speculation, which we quote from memory—a wrong thing to do. Impressed with the belief that consumption is communicable in foul air, and non-communicable in good air, he believes that the bacillus (a form of bacteria) which conveys the disease retains its virulence more in foul air than in pure air, and is thus better able to make a lodgment in the human system. —Contemporary Review.