Excerpt from Course of Hygiene for the Use of Hongkong Schools Carbonic Acid Gas - This gas though present in very small quantities is very important. It is one of the products of respiration and of combustion. All animals breathe out a certain quantity of this gas and the burning of anything such as wood, coal, oil, increases the amount of this gas. The oxygen which is used up in the process of breathing is replaced by this gas. 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.