INFLUENCE OF WORK 



499 



of carbon dioxide per kilogram of body-weight and hour under 

 such conditions. It is necessary to point out that this is not rest 

 in the ordinary sense of the word ; such muscular relaxation requires 

 the constant exercise of the will in the man who is awake and the 

 subject of observation. For this reason the data already given 

 for the discharge of carbon dioxide by male and female children 

 at different ages are to be considered normal ; the greater muscular 

 tone, even the restlessness, of the boy is a natural characteristic 

 which distinguishes him from the girl. 



More muscles are brought into activity in the standing than 

 in the sitting posture, and more in the sitting posture than in the 

 prone position. The differences are demonstrated by the increase 

 in the respiratory exchange, the temperature of the body, and in 

 the sensations of effort and fatigue. Although the first careful 

 experiments upon these questions were performed in this country 

 by E. Smith, the most exact investigations have been carried on 

 abroad, chiefly by Zuntz and his pupils and Johansson. E. Smith 

 found that a man discharged 161*6 c.c. of carbon dioxide per minute 

 when he was asleep, 569- 5 c.c. when he was walking at a rate of 

 two miles (3048 metres) an hour, and 851-2 c.c. when he quickened 

 the pace to three miles (457 T 9 metres) per hour. The most marked 

 increase, to 1581*9 c.c. per minute, was produced by work upon 

 a treadmill. 



The more recent observations have been made upon men, 

 horses, and dogs in the condition of rest, work of different kinds, 

 and rest immediately following work. A comparison of the effect 

 of walking upon level ground with the ascent of an incline was 

 made by Katzenstein, and the following results were obtained for 

 the respiratory exchange of three individuals. 



Johansson found that the output of carbon dioxide increased 

 with the load and the number of contractions in a given time, but 



