1312 



PHYSIOLOGY 



perfectly flaccid, breathing rapidly, or may go to sleep. On cooling 

 they at once become more vigorous and perform active move- 

 ments in their cage. The same effects of changes in the external 

 temperature are familiar in ourselves. The slackness and extreme 

 disinclination to violent exercise observed in hot moist weather, con- 

 trasted with the stringing up of the tone of the muscles which follows 

 exposure to cold, and which may be associated with voluntary exercise 







-w 



ff Kemp. cfeg. Cent. 



FIG. 543. Effect of variations in the external temperature on the C0 2 output 

 (per 1000 cm. 2 body surface) of warm-blooded animals. (C. J. MARTIN.) 



to keep ourselves warm, are indications of the important part played 

 by the muscles in determining the heat production of the body. As 

 a rule the immersion of a man in a cold bath for a minute or two 

 increases considerably his output of C0 2 . It is possible, however, 

 to sit in a bath and by an act of the will keep all the muscles in a state 

 of relaxation. Under these circumstances the temperature of the 

 body rapidly falls, and with it the rate of metabolism, as judged 

 by the output of carbon dioxide. 



This process of adjustment of the body temperature by variations 

 in the heat production, so long as it represents the only method, is 

 extravagant of energy directly the difference in temperature between 



