CHAPTER II 

 Carbon Dioxide and Regulation of Breathing. 



MY attention was first directed to the regulation of breathing by 

 a series of experiments carried out by Lorrain Smith and myself 1 

 as to the question whether, as had shortly before been asserted by 

 Brown-Sequard and d'Arsonval as a result of a very definite and 

 apparently convincing series of experiments, a poisonous organic 

 substance is given off in expired air. The results of our experi- 

 ments, which were made partly on man and partly on animals, 

 were entirely negative, and left no doubt in our minds that the 

 apparent positive results described were due partly to undetected 

 air leaks which led to animals being asphyxiated, and partly to 

 other experimental errors. In the human experiments we used an 

 air-tight respiration chamber of about 70 cubic feet capacity, in 

 which the air became more and more vitiated by respiration. 



The effects of the vitiated air on our breathing attracted our 

 attention specially. When the proportion of CO 2 in the air rose 

 to about 3 per cent, and the oxygen fell to about 1 7 per cent (there 

 being 20.94 per cent of oxygen and 0.03 per cent of CO 2 in pure 

 atmospheric air) the breathing began to be noticeably increased. 

 With further vitiation the increase in breathing became more and 

 more marked, until with about 6 per cent of CO 2 and 13 per cent 

 of oxygen the panting was very great, with much consequent 

 exhaustion. 



When the experiment was repeated, with the difference that 

 the CO 2 was absorbed by means of soda lime, there was no notice- 

 able increase in the breathing before the oxygen fell below about 

 14 per cent. When, finally, the CO 2 was left in the air, but oxygen 

 was first added so that the oxygen remained abnormally high 

 throughout, the panting was just the same as when ordinary air 

 was used. In short experiments in which the same air was 

 rebreathed from a large bag till we could no longer stand the 

 experiment we found that we had to stop at about 10 per cent of 

 CO 2 , whether oxygen was added or not, and that the oxygen per- 

 centage made no difference to the distress produced. In these 

 experiments there was only about 8 to 9 per cent of oxygen in the 



1 Haldane and Lorrain Smith, Journal of Pathology and Bacteriology, I, pp. 

 168 and 318, 1893. 



