Excerpt from Wiley's Health Series, Vol. 1: Nutrition Hygiene Physiology When is air impure? The air is impure when it contains too much or too little of any one of its natural constituents. For instance, if oxy gen, which is the most active substance in the air and the one on which the continuation of life depends, is diminished in quantity the air is impure. If, on the other hand, oxygen is increased in quantity the air is also impure. If the quantity of oxygen is decreased, then we have to take in a great deal more air to perform the functions of life; if it is increased the bum ing of the foods and tissues in the body would go on more rapidly and we should become ill and have fever. If there were no oxygen in the air we could not live; also, if the air consisted entirely of pure oxygen it would speedily cause us to die. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.