RESPIRATION. 541 



tion of CO 2 diminishes with the rise of external temperature from 4.4 until 

 the temperature reaches 14.3, when it rises slowly. These results have been 

 substantiated by the more recent investigations of Page, 1 who found in experi- 

 ments on dogs that the discharge of CO 2 was at a minimum at about 25 ; 

 that below this temperature the quantity increased as the temperature fell ; 

 and that above this temperature the discharge increased, and became greatly 

 augmented at temperatures of 40 to 42. At the latter temperatures the 

 increase may reach 3J times the normal, but the bodily temperature is also 

 increased. If the elimination of CO 2 at 23 to 24 be represented by 100 as 

 a standard, at 13 it will be about 128 ; at 10, 141 ; and at 18, 177. The 

 researches of Speck, 2 of Loewy, 3 and of Quinquaud 4 all show that external 

 cold increases respiratory activity, chiefly by causing involuntary muscular 

 excitement (shivering). If shivering and other forms of muscular activity be 

 absent, the exchange of O and CO 2 is unaffected or diminished, but when 

 present the increase of respiratory activity may amount to 100 per cent, not- 

 withstanding a fall of bodily temperature below the normal. 



Muscular activity is one of the most important of all the circumstances- 

 affecting the quantities of O and CO 2 exchanged. Involuntary excitement, 

 such as shivering, may of itself double the consumption of O and increase 

 by one-half the elimination of CO 2 , but the volitional effort may increase 

 the interchange even beyond these limits. Him, in investigations on 

 four men, noted during rest an hourly absorption of 30.2 grams of O, and 

 during work 120.9 grams; and Pettenkofer and Yoit, in similar studies, 

 found an increase of O from 867 grams during rest to 1006 grams during 

 moderate work, and from 930 grams of CO 2 to 1137 grams. In experiments 

 on the horse Zuntz and Lehmann 5 obtained the following results, which show 

 to what a marked extent the respiratory interchange may be increased by- 

 muscular activity : 



Liters per Minute. 

 O. C0 2 . ^- 



Eesting 1.722 1.570 0.92 



Walking 4.766 4.342 0.90 



Trotting 8.093 7.516 0.93 



Speck 6 has added some interesting facts to our knowledge of the effects of 

 muscular activity on the respiratory interchange. Thus, he found that the 

 increase of O and CO 2 reaches a maximum before exertion reaches its maxi- 

 mum ; that the increase for the same amount of work can be varied by chang- 

 ing the position of the body ; that if a given amount of work be divided into 

 two equal parts, the increase of respiratory activity during the first period is 

 greater than during the second ; that the greater the increase of CO 2 , the less,. 



1 Journal of Physiology, 1879-80, vol. 2, p. 228. 2 Loc. cit. 



3 Pfluger's Archiv f. Physiologic, 1890, vol. 46, pp. 189-224. 



4 Compt. rend., 1887, vol. 104, pp. 1542-1544. 



5 Journal of Physiology, 1890, vol. 2, p. 396. 



6 Deutsches Archiv f. klin. Med., 1889, vol. 45, pp. 460-528. 



