192 



RESPIRATION 



diminished at the lowered pressure, and were thus led to the theory 

 that the acidosis of high altitudes is due to diminished formation 

 of ammonia by the liver as a consequence of anoxaemia. 



The question was again taken up in a series of experiments in 

 steel chambers by Kellas, Kennaway, and myself, in which care- 

 ful measurements were made of the excretion of acid and am- 

 monia.*^ We found that even with a comparatively slight diminu- 

 tion of pressure there was a great diminution in the excretion of 

 acid and ammonia, and the urine passed to the alkaline side of 

 neutrality. The true explanation of the supposed acidosis then 

 revealed itself to us. The kidneys and liver were responding quite 

 normally, but to an alkalosis, this alkalosis being produced by the 

 increase (largely masked) of breathing caused by the anoxaemia. 

 A similar view of the supposed acidosis of high altitudes was 

 reached, on independent grounds which will be discussed below, 

 by Yandell Henderson.*^ 



The increased excretion of alkali and diminished formation of 

 ammonia lead gradually towards a compensation of the alkalosis 

 and simultaneous relief of the anoxaemia, this relief being due to 

 the increased oxygen supply to the lung alveoli, and to other 

 causes discussed in Chapters IX and X. But the final result is a 

 compromise. A certain small degree of anoxaemia and consequent 

 alkalosis still remains, as evidenced by a continued low excretion 

 of ammonia and other physiological symptoms and by the fact 

 that on removal of the anoxaemia there is a quite appreciable 

 immediate rise in the alveolar CO2 pressure, as was shown for 

 instance, when we breathed air enriched with oxygen after we had 

 become acclimatized on Pike's Peak. The extra excretion of alkali 

 comes to an end, however, as the kidneys cannot reduce the blood 

 alkali further without very serious alteration of the normal balance 

 of salts in the blood. 



The supposed acidosis is thus not an acidosis at all, but the in- 

 complete compensation of an alkalosis. The "adaptation" of the 

 blood so as to relieve the alkalosis and anoxaemia is also nothing 

 but an extension of the everyday adaptations by which alkalosis 

 and anoxaemia are continuously being prevented. The reason why 

 the adaptation takes so long at low atmospheric pressures is simply 

 that it takes a long time for the kidneys and liver to get level with 

 the very prolonged and considerable work thrown on them by 

 progressive increase in the breathing. They are, as it were, pursu- 



*" Kellas, Kennaway, and Haldane, Journ. of Physiol., LIII, p. i8i, 1919. 

 "Yandell Henderson, Science (N. S.), XLIX, p. 431, 1910; see also the series 

 of papers by Henderson and Haggard, Journ. of Biol. Chem., 1919.-1921 incl. 



