440 RESPIRATION. 



exhalation of carbonic acid during and immediately follow- 

 ing muscular exercise. In insects, Mr. Newport has found 

 that a greater quantity is sometimes exhaled in an hour of 

 violent agitation, than in twenty-four hours of repose. In a 

 drone, the exhalation in twenty-four hours was O30 of a cubic 

 inch, and during violent muscular exertion the exhalation 

 in one hour was O34. 1 Lavoisier recognized the great in- 

 fluence of muscular activity upon the respiratory changes. 

 In treating of the consumption of oxygen, we have quoted 

 his observations on the relative quantities of air vitiated in 

 repose and activity. 



Yierordt, in a number of observations on the human 

 subject, ascertained that moderate exercise increased the 

 average quantity of air respired per minute by nearly nineteen 

 cubic inches, and that there was an increase of 1*197 cubic 

 inches per minute in the absolute quantity of carbonic acid 

 exhaled. 2 



The following results of the experiments of Dr. Edward 

 Smith on this subject are very definite and satisfactory : 



In walking at the rate of two miles an hour, the exhala- 

 tion of carbonic acid during one hour was equal to the quan- 

 tity produced during If hour of repose, with food, and 2J 

 hours of repose, without food. 



Walking at the rate of three miles per hour, one hour 

 was equal to 2f hours with, and 3J- hours without food. 



One hour's labor at the tread-wheel, while actually work- 

 ing the wheel, was equal to 4J- hours of rest with food, and 6 

 hours without food. 3 



The various observers we have cited have remarked that 



ratory movements and the quantity of air passing through the lungs, and as we 

 have seen the quantity of carbonic acid in the expired air is increased in propor- 

 tion to the length of time that the air remains in the lungs, we can easily see the 

 source of error in his observations. 



1 MILNE-EDWARDS, Physioloyie, tome ii., p. 630. 



2 Cyclopcedia of Anatomy and Physiology, vol. iv., part i., p. 348. 



3 Op. cii. t p. 713. 



