114 METABOLISM AND NUTRITION 



ceptibly, and if one wishes wholly to exclude this effect it is necessary vol- 

 untarily to suppress all muscular movements and tensions. Under such 

 circumstances, that is, lying as quietly as possible, Johansson found the 

 C0 2 -excretion in himself to be about 20 g. per hour. Ordinarily while awake 

 we never observe muscular rest so complete as this, and hence when Johansson 

 merely lay resting in bed without special effort to suppress muscular move- 

 ments, his C0 2 -excretion rose to 25 g. per hour. In general we may say that 

 the respiratory exchange in a man not doing any real physical labor, and yet 

 not in absolute rest, is about forty per cent greater than in sleep. 



6. INFLUENCE OF THE SURROUNDING TEMPERATURE ON 



METABOLISM 



The cold-blooded and warm-blooded animals react very differently toward 

 changes in temperature. Whereas in the latter the respiratory exchange, which 

 may be taken as a relative expression of the total metabolism, rises when the 

 temperature falls, and falls when the temperature rises, in the former the 

 respiratory exchange varies directly with the external temperature. The fol- 

 lowing experimental results, after H. Schultz, may be given as an example 

 of the reaction of cold-blooded animals : 



It was first established by experiments from Pfluger's laboratory that when 

 the external temperature declines the metabolism of warm-blooded animals 

 increases over that characteristic of a medium temperature. By increasing 

 the heat production the body protects itself against the heat loss occasioned 

 by the cooling. Conversely, however, it is to be observed that a rise of the 

 body temperature also produces an increase in metabolism; which shows that 

 the energy of the oxidation processes in the warm-blooded also as well as in the 

 cold-blooded animals increases with the temperature of the organs. There is 

 here a fundamental agreement in the basal properties of living tissues in all 

 animals. The increase of metabolism accompanying a decline in the external 

 temperature is to be considered as a later acquirement on the part of warm- 

 blooded animals as something in fact which has been gradually evolved in 

 the special interest of a constant temperature (Pfliiger). 



How exact this adjustment of metabolism to external temperature may be 

 has been most beautifully shown by Eubner, as for example, in the following 

 experiment on the dog: 



