President's addkess. 27 



were much interested in physiological problems of respiration, 



and utilised this discovery to ascertain the average composition 

 of the air in the deepest recesses of the lungs. This air is usually 

 known as alveolar air, and Haldane called the last portion of the 

 expired air "alveolar air," though it is better to adopt the sug- 

 gestion of Keogh to call this part of the breath the "alveolar 

 expired air." By taking the samples from forcible expirations 

 at the end of inspiration and of expiration, Haldane obtained 

 two figures, and concluded that their average yielded the com- 

 position of average alveolar air. Haldane and Priestley* found 

 much constancy in this figure, so that they conclude that "for 

 each individual the normal alveolar C(X pressure appears to be 

 an extraordinarily sharply defined physiological constant." In 

 different persons, the figure varied, but remained constant in the 

 individual. These able experimentalists then carried out a 

 research to which I must refer you for details. They came to 

 the opinion that the volume of inspired air was doubled when 

 an increase of - 2% of an atmosphere occurred in the carbon 

 dioxide pressure in the alveolar air. By this statement, Haldane 

 and Priestley mean that the ventilation of the lung is increased 

 twofold when the percentage of carbon dioxide in the alveolar 

 air rises from 5*5% to 5'7%, or some similar alteration of 0"2%. 



A series of studies on the distribution of gases in expired air 

 was commenced by Lin hard and Keogh in 1911. Linhard, on 

 whom many experiments were made, has a slow, deep respira- 

 tion. In their investigation, they studied expired air not accord- 

 ing to quantity but to time. They collected samples at intervals 

 of a tenth or a fifth of a second as it was expired. They showed 

 that during work the composition of the expired air seems to 

 change continuously, that breathed later having a higher per- 

 centage of carbon dioxide. 



Our attention was called to this subject by repeated failures 

 to observe uniform figures for the tension of carbonic acid gas in 

 the alveolar air obtained from persons working in the laboratory 

 under easy conditions. We had supposed that the volume of the 



7 Haldane and Priestley, ibid., p. 253. 



