Page:Popular Science Monthly Volume 40.djvu/838

816 Now let us take the case of a person who sits in a closely shut up room, ten feet high, ten feet broad, and fifteen feet long, for five hours. At the end of that time he is breathing air which contains 1·2 per cent less oxygen than it ought to contain, but, what is far more serious, he is breathing some air which has already passed through his lungs, and which is charged with this special poison. Here is the great secret of the fatal mischief. Nature has got rid of the poison, thrown it out of the system, but the perverse occupant of the room insists on thwarting Nature, and, by means of his closed doors and windows, breathes in again, it may be a second time or a third time, the poison that has once been safely got rid of. Say that in twenty-four hours 500 cubic feet have passed once through the lungs, then in six hours our friend will have vitiated one quarter of that quantity, or 125 cubic feet—i. e., one twelfth of the whole air in the room (1,500 cubic feet). If he still goes on sitting in his study, at the end of nine hours he will have vitiated 187·5 cubic feet, or one eighth of the whole; or, if he has been unfortunate enough to have a friend sitting with him, then in six hours they will have tainted one sixth of the air; and of every mouthful of air they breathe after that time, one sixth of it must be supposed to be charged with poisons that have been already once got rid of, but are now being retaken into the system. Of course, this proportion of one sixth will not remain constant. Each breath expired will make the matter worse.

A few words seem necessary here for those who have never followed the changes going on in the body. We know that we are constantly building up new tissue of different kinds, and that this building up makes it necessary that the old tissue should be got rid of. The larger part of our food measures this change which is going on. If we take our daily food, liquid and solid, for twenty-four hours, as weighing about five pounds eight ounces (Hermann, page 233)—a large proportion being water—we may look upon about five pounds three ounces of this quantity as used for the making of new tissue, the other five ounces forming what is spoken of as exhausted ferments, and which, passing along the alimentary canal, is eventually rejected. Now, all the suitable part of the food, after undergoing various changes, which are necessary to prepare it for its passage from dead food into living tissue, finds its way into the blood; and when by means of the larger blood-vessels it reaches the very minute blood-vessels, called capillaries, it pours a part of itself out through the