igi2] Lafayette B. Mendel I49 



the Center along with a fall of the total amount in the blood. No 

 direct determinations of the condition of the blood in this respect 

 have been made. 



Determinations of the alveolar tensions of oxygen and carbon 

 dioxid during and at varying periods after muscular activity show 

 that with increasing intensity of work there is first a rise of CO2 

 tension, then a fall to and below normal. In the latter case the CO2 

 tension sinks still further after the cessation of the exercise and 

 may remain subnormal for over half an hour or even an hour. 



Review of the evidence as a whole leads to the conclusion that 

 during more vigorous exercise the main cause of the increase of 

 breathing movements is some catabolite (other than CO2) of the 

 working muscle. During moderate exercise the increase of CO2 

 tension of the blood is probably an adequate explanation ; the respi- 

 ratory condition of the organism would thus differ not only in 

 degree but also in kind with moderate and with more vigorous 

 exercise. 



Theory that the distress which is relieved by " second wind " is 

 due to excessive CO2 tension not well established by the evidence at 

 band, but worthy of further study. Bearing upon this question is 

 the effect of previous Inhalation of oxygen in lessening the distress 

 of maximal effort. 



Should not the measurement of respiratory power in physical 

 examination be extended so as to include not only the anatomic 

 features of ehest expansion and vital capacity, but also the ability of 

 the respiratory System to meet successfully the conditions of the 

 more vigorous forms of muscular activity? 



Yale University, 



New Haven, Conn. 



