RESPIRATION 369 



of CO 2 . It is during this condition that mountain sickness is pro- 

 duced. 



In the course of a day or two, or of several days, the mountain 

 sickness passes off if the altitude is not too great ; but the breathing 

 is only slightly increased further, as we found on Pike's Peak 

 (Figure 97) by analyses of the alveolar air. Further light on 

 acclimatization was afterwards thrown by Hasselbalch and Lind- 

 hard 7 in a series of observations during which they remained for 

 a number of days in a steel chamber at reduced pressure. They 

 found by direct measurement that after acclimatization the hydro- 

 gen ion concentration of the blood is approximately normal, thus 

 confirming Barcroft's conclusions from observations of the dis- 

 sociation curve of the oxyhaemoglobin of the blood. They also 

 found that the excretion of ammonia in the urine is distinctly 

 diminished; and this led them to the conclusion that the very 

 slight acidosis which presumably causes the increased breathing 

 is due to diminished formation of ammonia in the body. 



In a still more recent investigation 8 by Kellas, Kennaway, and 

 myself, we found that on exposure to a considerable diminution 

 of atmospheric pressure there is at once a very marked decrease 

 in the excretion of both acid and ammonia by the kidneys. The 

 urine may become actually alkaline to litmus. These observations 

 threw r a new and quite clear light on the increased breathing at 

 high altitudes. It became evident that the increased breathing is 

 primarily due simply to the stimulus of anoxaemia. This increased 

 breathing not only raises the alveolar oxygen pressure, but also 

 washes out an abnormal proportion of CO 2 and thus produces a 

 condition of slight alkalosis, to which the perfectly normal re- 

 sponse is a diminution of ammonia formation and in the acidity 

 of the urine, as explained in Chapter VIII. This response tends to 

 continue until the normal reaction of the blood is restored, owing 

 to reduction in the "available alkali" in the body. There is no 

 acidosis at any stage of the process ; the supposed acidosis is only 

 the compensation of an alkalosis. Nevertheless the process of 

 compensation is never quite complete. If it were so the excretion of 

 ammonia would return to its normal value on acclimatization, 

 whereas actually there is still, as shown by Hasselbalch and 

 Lindhard's observations, a slight but distinct diminution in am- 

 monia excretion. Moreover if the compensation were complete 



7 Hasselbalch and Lindhard, Biochem. Zeitschr., 68, pp. 265 and 295, 1915; 

 and 74, pp. i and 48, 1916. 



8 Haldane, Kellas, and Kennaway, Journ. of Physwl., LIU, p. 181, 1919. 



