28 President's address. 



inspired air was regulated so nicely that the tension of carbon 

 dioxide in the alveolar air remained practically constant from 

 minute to minute in any individual not performing heavy work 

 and breathing in a natural manner. We were surprised to 

 obtain figures varying - 5%, and generally lower than those 

 noted in Europe. A gas- burette was arranged by which a series 

 of samples of alveolar expired air could be obtained. With this 

 method it was possible to obtain exactly 10 c.cin. in each sample. 

 In this way it became possible to collect ten samples of alveolar 

 expired air, five at the end of inspiration and five at the end of 

 expiration, and to obtain the average figure by two duplicate 

 analyses. The method was accurate when the samples were taken 

 within a sufficiently short period of time to avoid any material 

 change in the barometric pressure and in the temperature. 

 The results showed a similar variation in the range of tensions 

 of carbonic acid gas. It was thus evident that the tension or 

 percentage of carbon dioxide in the alveolar expired air of per- 

 sons moving easily about a room was by no means constant, but 

 varied over a range approximately 10% of the tension. These 

 variations did not seem to be accompanied by such great altera- 

 tions in the depth of inspiration as might have been expected 

 from our knowledge of the results obtained by Haldane and 

 Priestley. A perusal of the original publication showed that the 

 individual figures obtained by Haldane and Priestley showed a 

 much wider range of difference than might have been supposed 

 from the wording of their conclusions. 



While we were engaged in the work which has been in part 

 published by Dr. Wardlaw and Miss E. Pinkerton, Haldane 

 published some further results as a consequence of some Ameri- 

 can studies on the "dead space" which raised doubts as to the 

 soundness of the original contention as to the uniform composi- 

 tion of the last part of the expired air. In this publication,* 

 Haldane recorded a series of observations showing how constant 

 was the tension of alveolar carbon dioxide. He made use of the 

 fact "that the frequency of breathing may be varied within wide 



Amer. Journ. Physiol., xxwiii., p. 20, 1915. 



