Page:Popular Science Monthly Volume 11.djvu/333

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ATMOSPHERIC PRESSURE AND LIFE.

must result insufficient respiration, or, more accurately speaking, insufficient absorption of oxygen." "The quickening of the respiration, which tends to offset the evil, is insufficient," says Martins, "for it would have to be twice as frequent, and have double amplitude, in order to compensate the diminution in the quantity of air inspired." Finally, Dr. Jourdanet adds that, "the pressure being reduced, the oxygen must be dissolved in the blood in a less proportion:" hence a pathological state analogous to anæmia, and which he calls anoxy-hœmia.

These ideas have been met with many objections. In reply to De Saussure it was said that the atmosphere, even at half-pressure, contains a great deal more oxygen than is needed for respiration; and in reply to Jourdanet that, according to the researches of Fernet, oxygen in the blood being in the state of combination, and not of solution, its quantity does not depend on barometric pressure.

My own experiments show that De Saussure and Jourdanet are right. They further prove the sagacity of Jourdanet in recognizing in the inhabitants of the Anahuac plateau the injurious influence of low pressure which, though not perceptible in the state of health, reveals itself on the slightest attack of disease. I need not detail here the long series of experiments which have led me to conclude that the symptoms following diminished pressure, whether slowly or rapidly applied, are simply the result of a diminution of the oxygen in the blood; in a word, that they are nothing but a sort of asphyxia in the midst of the "pure and invigorating mountain-air."

Still I may repeat here an experiment which can be performed wherever we have a pneumatic apparatus; this experiment clearly proves that the lessening of the barometric pressure is of no account, mechanically, in the production of the phenomena. These are the result rather of chemico-physical action, the blood not being sufficiently charged with oxygen.

We place a sparrow in the pneumatic bell-glass A (Fig. 1), which communicates with the manometric tube C E, The pressure is gradually lessened by means of the tube B. When the manometer shows only 30 centimetres' pressure in the bell-glass, the bird gives pretty serious evidence of suffering; at 20 centimetres it totters, reels, and falls upon its side; at 18 centimetres it struggles violently, and would die in a few seconds, were I to leave it in this situation. So I quickly place at a an indicator, to show the height attained by the mercurial column, and, opening the cock D, I introduce into the bell-glass not air, but oxygen from the India-rubber bag O. At once the bird becomes himself again. I let it breathe a little while, and again I diminish the pressure as before. But now we reach 30 centimetres, 25 centimetres, without difficulty; not till we reach 20 centimetres does the bird appear to show some little signs of discomfort; we reach 13 centimetres, a', a pressure much less than before, and yet the