WHEN OXYGEN KILLS

Greymouth Evening Star, 26 September 1933, Page 3

WHEN OXYGEN KILLS

INTERESTING EXPERIMENTS. The schoolbooks tell us that oxygen is necessary to life, and that carbon dioxide kills. This is true enough, in general. But there are circumstances when oxygen is fatal and when carbon dioxide will save life. What the circumstances are has long been the subject of .study by Dr. J. Willard Hershey, of McPherson College, Kansas. From a report of his published in “Nature” it is clear that if the atmosphere were different in composition from what it is-there might, be no life of the type we know. Dr. Hershey first attracted attention by proving that such small animals as rats, pigeons, cats, guinea pigs and monkeys can live in a medium of air under control, but that they die within two to five days in pure oxygen. While this is startling enough to anyone who has ever seen, oxygen administered as a last resort, it is still more startling to discover that even the rare gases, argon,helium, neon, krypton and carbon dioxide, which comprise only 1 per cent, of the atmosphere are essential to the maintenance of life. For example, Dr. Hershey’ made a mixture of nitrogen (79 Tier cent.) and, oxygen (21 per cent) and tried this on’ his animals. Except for the absence of the rare gases it was like the air we breathe. In ten experiments the test animals all died. The conclusion is irresistible hat the rare gases are indispensable. On the other hand, synthetic atmospheres were prepared which were more effective in sustaining life than normal air. Thus in an artificial atmosphere consisting of 79 per cent, helium and 21 per cent, oxygen animals seem to be better off than in ordinary air. The percentage of helium may be as low as 50 per cent, and still the ani-. mals thrive well. j

Pure gases are invariably fatal. Animals die in 36 minutes in pure hydrogen; in 6 minutes in nitrogen, which is ■what we would expect; in 3 minutes in argon; in 1 minute and 40 seconds in neon; in 2 minutes and 40 seconds in helium; in 10 minutes in nitrous oxide, and in 55 seconds in carbon dioxide.

An atmosphere composed of 0.03 per cent carbon dioxide (the amount present in air) and 99.7 per cent, oxygen is as fatal as pure oxygen. Other mixtures of the same gases are scarcely

' better. What, then, is the use of carbon dioxide? To flush out toxic substances from the lungs by making us breathe deeply and thus to combat respiratory failure. It is evident that a promising field of investigation has been opened. The physician will surely wish to see these studies pursued. He has been using oxygen tents with success in the treatment of penumonia. Other diseases, as Dr. Hershey suggests, may yield to argon and helium.