500 



THE RESPIRATORY EXCHANGE 



the sensation of fatigue bore no direct relation to the output of 

 carbon dioxide. The effect of speed is well shown by the following 

 observations made by Zuntz and Lehmann upon horses. 



These figures show not only the great increase produced in the 

 ventilation of the lungs and the respiratory exchange, but also 

 the absence of any alteration in the respiratory quotient. 



A bicycle ride at the rate of 827 feet (252 metres) per minute 

 or 9 miles (15 kilometres) per hour necessitated an absorption of 

 4674 c.c. of oxygen per metre of the distance traversed ; this 

 was increased to 5672 c.c. when the speed was quickened to 

 1165 feet (355 metres) per minute or 12J miles (21'3 kilometres) 

 per hour. This marked increase observed by Leo Zuntz is not 

 to be entirely attributed to the extra rate of riding, but in part 

 to the extra muscular effort necessary to overcome the resistance 

 of the air, a factor well known to all. 



It is a matter of general experience that practice makes the 

 performance of work easier, fatigue renders it more difficult. It 

 is also well known that at the commencement of exercise or 

 muscular work there is often absent even in the trained man that 

 smoothness in the co-ordination of the muscular contractions, 

 respiration and circulation, which comes after a short time, and 

 is expressed in the colloquial language of the labourer as " getting 

 into the swing of the work." The adaptations involved are no 

 doubt very complex, but here can be discussed only the respira- 

 tory exchange. There are indeed quantitative, if not qualitative 

 changes, in the respiratory exchange which appear to agree with the 

 experience of the man, and even in animals such a condition obtains. 

 Thus Zuntz and Lehmann showed that when a horse was made to 

 perform a moderate task of considerable duration, he worked after 

 a short time more economically, discharged less carbon dioxide, and 

 absorbed less oxygen than in the early stages of the work. 



