128 



J. Lindhard. 



In quite recent years an extensive and interesting work has 

 been carried out by English physiologists, especially Haldane and 

 his collaborators, in order to show the alveolar carbonic acid ten- 

 sion's decisive importance as the regulator of the ventilation of 

 the lungs. 



To be able to carry out a large number of analyses under 

 all possible conditions, without being bound to the laboratory, 

 Haldane and Priestley ^ have indicated and developed a rapid and 

 apparently convenient method of directly determining the alveolar 

 air. In a later work by Haldane and Fitzgerald'^ the mode of 

 procedure is still further simplified. My objections to this method, 

 as already shown, are, in the first place, that it is doubtful whether 

 we obtain normal alveolar air by this method, and secondly, that 

 even in the hands of an experienced investigator considerable inac- 

 curacies may be introduced, as can readily be shown, and lastly, 

 that there will always be greater uncertainty in the single deter- 

 minations on this method than by calculation according to Bohr's 

 formula of an average sample. In spite of these objections, however, 

 I quite admit that with some experience and with a sufficiently 

 large number of analyses, we might be able to demonstrate the 

 variations in the composition of the alveolar air. 



After their investigations on their own alveolar air, Haldane 

 and Priestley began with ascertaining, that the alveolar carbonic 

 acid tension may well vary individually but is nevertheless a con- 

 stant magnitude for each individual, independent of practically all 

 physiological encroachments, with the exception of excessive changes 

 in the air-pressure. The total volume of air respired is regulated 

 by the action of the carbonic acid on the respiratory centre, in 

 such a way, that the carbonic acid tension, when its state of equili- 

 brium is altered, tends to return again to its individual standard 

 value. 



In the above-mentioned work of Haldane and Fitzgerald it is 

 shown that the alveolar carbonic acid tension lies at a somewhat' 

 different level or in different zones, according to age and sex. 

 For men the following values are given: 



Maximum 44-5 mm. 

 Minimum 326 — 

 Average 39-2 — 



From later investigations Haldane has seen, however, that the 

 constancy is not absolute, that the carbonic acid tension like other 



1 The Journal of Physiology. Vol. XXXII, 1905. 



2 ibid. 



