Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. This is an OCR edition with typos. Excerpt from book: THE BEARING OF SUBWAYS ON HEALTH A study of all the effects of subway conditions on public health would form an extremely difficult inquiry and obviously can only be dealt with here in a most general manner. Vital statistics are not available to show the state of health of persons who use subways as compared with those who do not, nor are facts at hand to indicate differences in public health which can, with certainty, be ascribed to underground railways. For practical purposes, it is probably safe to assume as a groundwork of inquiry that if subways produce evil effects upon the health of the traveling public, these effects are due to overcrowding or some harmful quality of the subway air. CHAPTER II CHARACTERISTICS OF GOOD AIR AND BAD AIR THE ATMOSPHERE OF THE OPEN COUNTRY So far as known, there is only one constituent of the atmosphere which is directly useful to living beings and this is oxygen. The other gases are not immediately necessary, although they perform many indispensable functions in the economy of nature. The essential act of respiration is an absorption of oxygen and a production of carbon dioxide. It is natural to think of this exchange as one which takes place only in the lungs, but it is really common to all the myriad cells of the body. The lungs act simply as central exchange depots; the distant cells are the real laboratories. The principal gases of the atmosphere are present in a mechanical mixture and not in chemical combination with one another. A portion of the oxygen may be abstracted without affecting the other constituents and other gases may be added without affecting the oxygen. Oxygen has always the same properties whether it is freshly prepared or not. Fresh air is simply air which is uncon- taminated. Were it not tha...