130 



J. Lindhard. 



It is worth noting that the changes in the carbonic acid ten- 

 sion on the ascent occurred so to speali on the way; a couple of 

 liours afterwards, the organism already showed itself adapted to the 

 new conditions. On the descent, on the other hand, it took a week 

 for the carbonic acid tension to return to its former level, and the 

 rise was irregular. It is further worth noticing, that the fall in the 

 tension on ascending the mountain is out of all proportion much 

 greater than in the experiments under corresponding changes of 

 pressure at the Lister Institute in London. 



London Zermatt London Monte Rosa 



Barom. 628 633 494 4435 



CO 2- tension 371 342 359 285 



When we remember, that the great change on ascending to the 

 high level happens almost as quickly as the small change in the 

 pneumatic steel-room, and that it remains much longer, one gets 

 the impression that other and stronger forces than the reduced air- 

 pressure have played some part in these results. 



The effect of reduced oxygen tension was also studied by Hal- 

 DANE and PouLTON \ wlio fouud that hyperpnoe occurs on a rapid 

 fall of the proportion of oxygen. This hyperpnoe is due, however, 

 not directly to the lack of oxygen but to the already present car- 

 bonic acid, the "threshold value" of which is reduced, owing to the 

 lactic acid or other substances produced as the result of the lack of 

 oxvgen. Removing the preformed carbonic acid by forced respiration, 

 we can even produce apnoe in spite of distinct lack of oxygen. 

 Thus, the oxygen or lack of oxygen cannot have a direct effect on 

 the respiratory centre, and just as little the abnormal products of 

 metabolism, which owing to the lack of oxygen appear in the blood 

 and tissues, especially lactic acid. They affect the centre indirectly 

 by reducing the threshold value of the carbonic acid tension. The 

 formation of these abnormal products of metabolism is a very gradual 

 process; if the fall in the oxygen tension proceeds with a suitable 

 slowness, so that the preformed CO о obtains time to be eliminated,' 

 no hyperpnoe occurs; a fall of still longer duration will, on the 

 other hand, give the abnormal metabolic products time to accumu- 

 late, so that the centre is stimulated and the threatening symptoms 

 of lack of oxygen are averted. 



The paramount importance of the carbonic acid tension for the 

 respiratory centre's activity is also shown by the investigations of 

 Pembrey and Alle№ on the respiration of Cheyne-Stokes type. 



1 The Journal of Physiology. Vol. XXXVII, 1908. 



- Proceedings of the Physiological Society, 21. Jan. 05. Journal of Physiology. 

 Vol. XXXII. 



