Contribution to the Physiology of Respiration under the Arctic Climate. 137 



organ is reduced. Zuntz and Loewy's contention ^, that the increased 

 total volume of air respired at high elevations is due to certain 

 "excitations" peculiar to the mountain climate, since we cannot 

 assume that the centre changes in sensibility, is therefore scarcely 

 maintainable. It may be maintained where there is a question of 

 reduced carbonic acid tension in conjunction with increased total 

 volume of air respired; but when, as on my "cold days", we have 

 increased carbonic acid tension and reduced total volume of air 

 respired, this explanation is of no use to us. 



As mentioned, the changes in the alveolar carbonic acid tension 

 due to fluctuations of the barometer do not seem to influence the 

 total volume of air respired. In other w^rds, it appears as if varia- 

 tions in the carbonic acid tension as the result of changes in the 

 total pressure, are without influence on the respiratory centre. My 

 material is admittedlj' not suited for wide-reaching conclusions in 

 this direction, at the most I can only give suggestions; but it is 

 very fortunate, that the investigations of the English physiologists 

 also support these vieAvs. 



As mentioned on p. 129 Haldane and Boycott have found, that 

 the carbonic acid tension remains constant until a pressure of 550 

 mm. in experiments of short duration, as also that, if sufficient 

 oxygen is present, the pressure can be still further reduced without 

 reducing the carbonic acid tension. There is indeed nothing remark- 

 able here; the organism must have time to accomodate itself to the 

 altered conditions. And the accomodation shows itself as soon as 

 the experiment is prolonged. Haldane and Poulton have therefore 

 come to the result that, given a suitably slow change in the pres- 

 sure, the carbonic acid tension may be very greatly reduced without 

 the total volume of air respired being changed. It is only with a 

 still slower fall that there is time for the accumulation of abnor- 

 mal metabolic products, which by reducing the threshold value of 

 the carbonic acid exercise some influence on the centre; but it seems 

 to me undoubted from the foregoing, that the carbonic acid tension 

 may be reduced very considerably without aff'ecting the respiratory 

 centre, when the fall in the tension is a result of reduced total pres- 

 sure. It is quite possible, therefore, that the low alveolar carbonic 

 acid tension at high altitudes may, in part at any rate, be due to 

 the low air-pressure; but the accompanying, increased total volume 

 of air respired can certainly not be due to this. It might however 

 be a result of want of oxygen, by which the threshold value of the 

 carbonic acid tension is altered. But is there any lack of oxygen 



' Höhenklima und Bergwanderungen Kap. XI. 



