484 



THE RESPIRATORY EXCHANGE 



The rate and depth of respiration does not, as Pfliiger showed, 

 determine the rapidity of combustion in the body ; the tissues set 

 the pace, and apart from the increased muscular activity of the 

 respiratory muscles, rapid breathing does not bring about a greater 

 total exchange of gases than slow breathing. This is demon- 

 strated in an interesting way by Pniiger, who combined the ap- 

 parently discordant results obtained by Lossen and Berg, and 

 showed that the mean values were practically the same. 



Carbon Dioxide Discharged in Fifteen Minutes. 



The rate and depth of breathing vary greatly in different 

 individuals, in some respiration is deep and slow, in others shallow 

 and frequent. As an average figure for an adult man may be given 

 500 c.c. for each respiration, when the frequency is 16 per minute ; 

 these data, however, are not of much value, for the range of variation 

 in healthy men is very great. Haldane and Priestley have recently 

 shown that when the respirations are increased in frequency they de- 

 crease in depth, and vice versa ; so that for the same individual the 

 percentage of carbon dioxide in the alveolar air remains unaffected 

 by alterations in the frequency of breathing, provided that the respi- 

 rations are not forced. The following table shows these results. 



