Respiration. 93 



higher than this ; the largest amount T ever obtained was 

 145 cubic feet per hour. Assuming that the animal breathes 

 ten times per minute, the amount of each inspiration may 

 be taken at 230 cubic inches. It is to be noted that the 

 amount of air expired, even under apparently identical con- 

 ditions, is liable to great variation. We have no means of 

 knowing the amount of the residual, reserve, or comple- 

 mental air which may be used. 



Respiratory experiments have been made on nearly all 

 animals. I will principally confine my remarks to the 

 horse, on Avhich some very extended observations have 

 been carried out. 



100 parts of inspired air contain ; 

 Oxygen - - 20-96 



Carbonic acid - - -03 



Nitrogen - - - 79-01 



100 parts of air collected from the lungs during repose contain : 

 Oxygen - - - - 18 96 



Carbonic acid - - 1"25 



Nitrogen - - - 79*01 



Undetermined gases - *78 



The expired air has thus lost 2 per cent, of its oxj^gen. 

 and has gained 1*22 per cent, of C0 2 . In other words, it 

 leaves the lungs containing about forty times more C0 2 than 

 when it entered, in addition to which there is added § cubic 

 foot of gases of unknown composition — probably a mixture 

 of nitrogen, hydrogen, and marsh gas. 



More oxygen is absorbed than C0 2 expired, and my obser- 

 vations show that the respiratory quotient for the horse 

 at rest is -69, a figure which is much lower than that 

 generally quoted, viz., - 9 (see p. 84). 



If we take the C0 2 of repose at 1£ cubic feet per hour for 

 a horse, the carbon of this would be equal to 293 grains, or 

 14f ozs. in 24 hours. 



These results, however, do not agree with those obtained 

 by Zuntz and Lehmann in Germany.* The horses used by 



* Ellenberger's ' Physiologie.' 



