370 RESPIRATION 



there would be no extra breathing caused by the immediate effect 

 of the anoxaemia. Actually there is still a slight amount of extra 

 breathing from this cause, since on raising the alveolar oxygen 

 pressure there is an immediate, though comparatively slight, rise 

 in the alveolar CO 2 pressure, as we found on Pike's Peak when a 

 mixture rich in oxygen was breathed in place of ordinary air. 

 The evident reason why the compensation does not become more 

 complete is that if it were made more complete the normal com- 

 position of the blood would be very seriously altered; and such 

 alterations tend to be resisted. The compensation thus represents a 

 compromise. 



A similar interpretation of the apparent slight acidosis of high 

 altitudes was reached on independent grounds by Yandell Hender- 

 son, and published shortly before our paper appeared. 9 As already 

 mentioned in Chapter VIII, he and Haggard made the very 

 important discovery that with prolonged and very excessive 

 ventilation of the lungs (thus producing great alkalosis) the 

 available alkali or "alkaline reserve" of the blood diminishes 

 greatly. A similar diminution occurs at high altitudes, and Hen- 

 derson attributed it to the increased breathing produced by the 

 anoxaemia, and was thus the first to identify its true nature as a 

 compensatory response to the alkalosis produced by the increased 

 breathing. 



It is evident that the compensatory change in the available 

 alkali of the blood and whole body tends to make increased breath- 

 ing possible with a minimum stimulus from actual anoxaemia. 

 The anoxaemia tends, therefore, to be relieved. In other words a 

 process tending to acclimatization has occurred. It will be noted 

 that the phenomena have been interpreted on what is usually 

 called a teleological basis, though no conscious adaptation of 

 means to end is implied, but only a tendency of the living body to 

 maintain its normal standards. The justification for this mode of 

 interpretation, and the demonstration that it constitutes the neces- 

 sary scientific basis of physiology, will be postponed to the next 

 chapter. 



In connection with the Pike's Peak expedition Miss FitzGerald 

 carried out a large series of investigations of the alveolar air of 

 persons living permanently, and therefore fully acclimatized, in 

 towns and villages at different altitudes in or near the Rocky 

 Mountains. At a later date further observations were made at 



9 Yandell Henderson, Science, May 8, 1919; and Haggard and Henderson, 

 Journ. BioL Chem., XLIII, p. 15, 1920. 



