236 RESPIRATION 



increasing the weight the amount of work done by the subject 

 could be raised. It was not possible to measure the actual work 

 done in mechanical units, but we could do so in physiological 

 units by observing, by means of the small gas meter, the effect 

 on the oxygen consumption of the subject per minute. What we 

 term "moderate work" in the tables below was sufficient to raise 

 the total oxygen consumption to one and a half times its resting 

 value, while "severe work" doubled the resting oxygen consump- 

 tion. Work which doubles the resting oxygen consumption is only 

 equivalent to walking on the flat at two miles per hour, and does 

 not sound particularly severe, but we found it sufficiently tiring 

 when it was performed by one arm only, and kept up for half an 

 hour at a time. 



The lower part of Table III shows the results of the work ex- 

 periments. These results are very striking : for the arterial oxygen 

 pressure was on an average 4.4 per cent, or 32 mm. of mercury, 

 above the alveolar oxygen pressure, and in two experiments was 

 8.5 and 15.6 mm. above the oxygen pressure of the inspired air 

 (allowing for aqueous vapor). 



In the last experiment on the table the effects of muscular work 

 and low oxygen in the inspired air were combined. It will be seen 

 that the arterial was 33.5 mm. above the alveolar oxygen pressure, 

 whereas with a low oxygen in the inspired air and no work the 

 arterial never exceeded the alveolar oxygen pressure by more than 

 13 mm. As already mentioned, it was noticed that when work 

 was done while a low oxygen percentage was being breathed the 

 lips and face lost the bluish color due to the low oxygen, and 

 became of a normal red color. It was also noticed many years ago 

 by Loewy^^ that even a slight muscular exertion produced a 

 marked improvement in the subjective symptoms of want of oxy- 

 gen in a steel chamber at low atmospheric pressure. Our results 

 on the arterial oxygen pressure during muscular exertion furnish 

 an evident clue to these observations. 



In a former chapter I have referred to some of the results of 

 the expedition to Pike's Peak undertaken in 191 1 by Professors 

 Yandell Henderson and Schneider, Dr. Douglas, and myself. ^^ 

 Part of our object was to determine whether the want of oxygen 



" Loewy. Untersuchungen u. d. Respiration und Circulation, Berlin, 1895, 

 p. 16. The fact that Geppert and Zuntz {Pfliiger's Archiv, XLII, p. 189, 1888) 

 found a little more oxygen in arterial blood during work than during rest may 

 point also in the same direction. 



" Douglas, Haldane, Yandell Henderson, and Schneider, Phil. Trans. Roy. Soc, 

 (B) 299, p. 195, 1913. 



