20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 60 



Sweating and slight headache are the only abnormal results of the 

 short exposure to such percentages of C0 2 . 



If the CO, be removed from the blood and tissues by a preliminary 

 period of increased ventilation of the lungs, analyses of the pul- 

 monary alveolar air taken at the breaking point, show that when the 

 partial pressure of C0 2 is lower, a lower partial pressure of oxygen 

 can be borne, and vice versa ; for example, the breaking point 

 occurred with 6.6 to 6.9 per cent C0 2 , and II. I to 9.1 per cent 2 ; 

 with 5.5 to 5.9 per cent C0 2 and 5.8 to 3.7 per cent C) 2 ; with 8 to 

 10 per cent C0 2 and 30 to 50 per cent 2 . 



Oxygen-inhalation notably increased the power to do work with 

 the breath held, and the partial pressure of C0 2 in some cases rose 

 to 11 per cent of an atmosphere before the breaking point occurred. 1 



One subject, with the breath held, ran 113 yards in J^Ys seconds 

 after ordinary breathing, 150 yards in 35^3 seconds after deep breath- 

 ing, and 256 yards in 62^5 seconds after deeply breathing oxygen. 



As some reserve of energy must be kept for collecting the sample 

 of pulmonary air, it is clear that the percentage of CO, must rise 

 higher than 1 1 per cent in those who run to the utmost limit of 

 endurance with the breath held. 



These experiments make it quite clear that while the lungs 

 normally contain 5 to 6 per cent of C0 2 , at sea-level pressure, it is 

 no less certain that they may contain more than this amount when 

 the breath is held during any effort, and such temporary exposures 

 have no ill effect. 



Speck found that the inhalation of 7 per cent C0 2 produced great 

 hyperpnoea, but he managed to endure it for 2.5 minutes. On breath- 

 ing an atmosphere containing 11.5 per cent he found that the first 

 breath was uncomfortable — there resulted headache, sweating, dim- 

 ness of vision, and tremors. He could hardly endure the inhalation 

 for a period of one minute. On inhaling 5.4 per cent C0 2 he 

 exhaled 6 per cent and still maintained a respiratory exchange by the 

 intensity of his breathing ; with 7 to 8 per cent C0 2 inspired, 7 to 

 8 per cent was expired, and the output of C0 2 from the body was 

 checked. The symptoms of poisoning begin when this happens ; the 

 lower percentages, which cause no retention of C0 2 in the body, 

 have no effect other than the production of hyperpnoea. Low}' 

 found with 6 per cent C0 2 considerable dyspnoea and with 8 per cent 

 very great dyspnoea. Emmerich recorded that the inhalation of 8.4 

 per cent C0 2 caused dyspnoea, a flushed face and headache in 10 



1 llill ami Mack, Journ. Phys., Vol. 40, 1910, p. 347. 



