Excerpt from The Light Side of Science Carbonic acid gas and its Story - Mechanisms Of breathing - Gills and lungs - Their respective functions in fishes. The fact that our chests rise and fall fifteen or sixteen times a minute in the act of respiration or breathing is so familiar that it almost escapes popular recognition through its practically auto matic continuous nature. Breathing is one of those actions, which, while absolutely essential for the maintenance of life, and which, performed for the most part unconsciously, yet lie somewhat under the control of the will. Physiologists call breathing a secondary automatic action, in order to distinguish it from those functions of the body with which we cannot interfere. The duties of digestion, the making of bile, the formation of saliva, the ow of tears, the expansion or contraction of the blood vessels - are acts which proceed independently of our will and consciousness, and they are undoubtedly performed all the more perfectly in that we have no need to concern ourselves about them at all. 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."