THE PHYSIOLOGY OF MUSCULAR WORK 237 



the muscles of frogs, as Bayliss has shown. There is no doubt 

 about the close association of dilatation of the cutaneous vessels 

 with a rise in the temperature of the body produced by muscular 

 work. Further observations, however, are necessary to explain 

 the means whereby muscular work influences the heart and 

 circulation. 



INFLUENCE OF MUSCULAR WORK UPON THE RESPIRATION 



Even during rest the differences in the rate and depth of breath- 

 ing of healthy men are considerable ; some men breathe slowly 

 and deeply, others take rapid and shallow respirations. The 

 " tidal air " may vary from 100 to 1000 c.c., and the total volume 

 of air breathed per minute shows a similar wide range, the deter- 

 minations ranging from 3000 to 9000 c.c. These figures have 

 been taken from the results of different observers ; x in addition 

 may be given a series ( 32 ) recently made upon sixteen subjects, all 

 of whom, with two exceptions, were medical students : 



1 See article Chemistry of Respiration, by M. S. Pembrey, iu 

 Physiology," edited by Schafer, vol. i., 1898, p. 748. 

 * Measured at 15 moist. 



Textbook of 



