Page:Popular Science Monthly Volume 40.djvu/842

820 is, therefore, first the good oxidizer (see M. Foster, page 628), the person who has good lung capacity, and especially a powerful heart to drive the blood swiftly; and, secondly, the person who trains well, whose tissue is healthy and firm and does not break down rapidly into waste—waste in his case not outstripping the powers of oxidation, and thus causing distress. On the other hand, the untrained man, who breaks down in the race with every symptom of distress, is the poisoned man—the man who formed waste quicker than he could oxidize it. In such a case it may be asked, Why are not the waste poisons passing into the blood from the tissues safely got rid of in the form of carbonic acid and water when the blood reaches the lungs? It seems difficult to escape from the conclusion (see Foster, p. 603) that these unoxidized waste products may, on occasion, pass the lungs without being got rid of. In the case of violent exercise, it would seem that the quickened heart and quickened breathing must come from the action of waste poisons, which, passing the lungs, reach the medulla and stimulate the nerve-centers, there not having been time, owing to the excessive quantity of waste produced, to reduce all the waste to the safe final products of water and carbonic acid, and therefore some part of the waste in an unoxidized state being carried past the lungs on to the nerve-centers. As regards the poisons we rebreathe from the air, it is, of course, rather a surprising thing, if they entered the circulation, that they should not be oxidized in the blood when we think of how they must be surrounded by the oxygen that the blood has received from the air. But active as oxygen is—in its "nascent" state, just released from hæmoglobin—in the tissues after leaving the blood, there are reasons for thinking that this activity does not exist in the blood itself. Thus we are told that pyrogallic acid, which is an easily oxidizable substance, may pass through the blood without undergoing any change; and fresh blood, as we are told, has little oxidizing effect. This strange powerlessness of the oxygen in the blood increases the danger of these waste poisons. If they were oxidized in the blood we should be able probably to got rid of them quite harmlessly, as they would not be in the condition of poisons when they escaped from lungs and skin; but we may feel sure that there is some good reason why this can not take place. When they are once carried to the tissues, except in the case of persons taking plenty of exercise and leading a healthy life, there may be no superabundance of oxygen, but rather a deficiency, for all the work to be done.

Reviewing, then, what we have said, we seem to see three things: first, that so long as we have a sufficiency of oxygen, we get rid of a large amount of daily waste in safe and harmless forms; secondly, that when oxygen is withheld from us there are poisons in every part of our tissue of so deadly a character (either abnormally formed because oxygen is absent, or under ordinary circumstances neutralized by the supplies of oxygen present) as to take life in a few minutes; thirdly, that even when all is well, and our system is functioning under healthy conditions, we are still always breathing out from ourselves, through lung and through skin, certain dangerous poisons, which poisons, when we are living in bad air, we perpetually reabsorb into ourselves, to our own great hurt.

Nothing, however, that we have said satisfactorily explains the presence of these poisons which escape from the lungs and the skin. It seems hard to explain why, when Nature so successfully