542 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



proportionately, is the increase of O, so that the respiratory quotient rises 

 more and more, and to such an extent that the CO 2 contains more O than is at 

 the time absorbed ; and that the quantity of air respired is so intimately related 

 to the amount of CO 2 given off that he regards the quantity of this gas 

 formed as the regulator, as it were, of the degree of activity of the respiratory 

 movements. 



Griiber l states that while respiratory activity is proportional to the inten- 

 sity of muscular activity, " training " diminishes the quantity of CO 2 given 

 off for the same amount of work. Thus, taking 1 as a standard of the 

 amount of CO 2 eliminated during rest, he obtained the following ratios in two 

 series of observations : 



Climbing hills Climbing hills 



Resting. Walking. when not used when used to 



to it. it. 



First series 1 1.89 4.1 3.3 



Second series J_ 1.75 3.05 2.42 



Mean 1 1.82 3.07 2.86 



Training, therefore reduces the output about 20 per cent. 



The elimination of CO 2 is about one-fifth less during sleep than while 

 awake and quiet ; from one-fifth to one-half greater during ordinary exertion ; 

 from two to two and a half times greater during violent exercise; and about 

 three times greater during tetanus. 



During hybernation the absorption of O falls to ^- and the elimination of 

 CO 2 to ^ of the normal for the period of activity (Valentine). Relatively 

 more O is absorbed than CO 2 given off, hence the respiratory quotient falls, 

 reaching as low as 0.50 to 0.75. 



A diminution of the barometric pressure increases the respiration-rate and 

 the volume of air respired, but both Mosso and Marcet have shown that if 

 allowances be made for the increase of volume of the air at the lower pressure, 

 the actual volume respired is less. Conversely, an increase of pressure lowers 

 the rate and the volume of air respired. Extremes of pressure severely affect 

 the respiratory and other functions (p. 559). 



The integrity of the nervous apparatus which governs the metabolic pro- 

 cesses in the tissues is obviously of fundamental importance. If the efferent 

 nerve-fibres of a muscle be cut, the interchange of O and CO 2 at once sinks, 

 as illustrated by the following results obtained by Zuntz : 



O consumed. C0 2 given off. 



Before section 13.2 c.c. 14.4 c.c. 



After section 10.45 c.c. 10.1 c.c. 



After section (less) 2.75 c.c. 4.3 c.c. 



The consumption of O was therefore lessened about 20 per cent., and the 

 formation of CO 2 about 30 per cent. 



After section of the spinal cord in the dorsal region Quinquaud 2 obtained 



1 Zeltschrift f. Biologie, 1891, vol. 28, pp. 466-491. 



2 Compt. rend. Soc. Biologie, 1887, pp. 340-342. 



