loo CONTEMPORARY SCIENCE 



I shall not discuss pulmonary oxygen secretion now, 

 because the problem is still extremely obscure ; nor the 

 increased production of red blood corpuscles, which is a 

 slow process requiring weeks for completion, and play- 

 ing no considerable part in the matter particularly before 

 us. 



We will fix our attention upon the fact that both the 

 alveolar CO 2 of the pulmonary air and the alkaline re- 

 serve of the blood are reduced in accurate adjustment to 

 any altitude, or oxygen tension, to which a man is sub- 

 jected for a few days or even a few hours. This func- 

 tional readjustment is, I believe, of great significance in 

 relation to aviation, since it involves a larger volume of 

 breathing per unit mass CO 2 eliminated : it thus compen- 

 sates in part for the rarefaction of the air. 



But how is it brought about ? And why are the changes 

 of breathing gradual, when the changes of altitude and 

 oxygen tension are abrupt? The answer lies in part at 

 least in the mode of development, and the nature of that 

 acidosis of altitude to which I have referred. It is 

 scarcely necessary to remind you that, as L. J. Henderson 

 has shown, the balance of acids and bases in the blood, 

 its C H , depends upon the maintenance of a certain ratio 

 between the dissolved carbonic acid, H 2 CO 3 and sodium 

 bicarbonate, NaHCO 3 , or as Van Slyke terms it, the alka- 

 line reserve. On the basis of this conception the prevalent 

 view of acidosis is that, when acids other than carbonic 

 are produced in the body, the bicarbonate is in part neu- 

 tralized. The alkaline reserve is thus lowered, and the 

 carbonic acid of the blood being now in relative excess, 

 an increased volume of breathing is caused as an effort at 

 compensation. 



Recent investigations 6 by Dr. H. W. Haggard and 

 myself show that an exactly opposite process is likewise 

 possible. We find that whenever respiration is excited to 



6 Henderson and Haggard, Jour. Biol Chem., 1918, pp. 333 

 345, 355, 365. 



