870 METABOLISM. 



SON 1 upon human beings, teach us that if the muscular work is elim- 

 inated the metabolism during waking hours is not greater than in sleep. 



The action of light also stands in close connection with the question 

 of the action of muscular work. It seems positively proven that metabo- 

 lism is increased under the influence of light. Most investigators, such as 

 SPECK, LOEB, and EwALD, 2 consider that this increase is due to the move- 

 ments caused by the light or an increased muscle tonus, and in man an 

 increase in metabolism under the influence of light with complete 

 rest has not been observed. Divergent results have been obtained in 

 animals, and our knowledge of the truth is not yet complete. 3 



Mental activity does not seem to have any influence on metabolism 

 according to the means at hand for studying this influence. 



The Action of the External Temperature also stands in close relation 

 to muscular work, namely to the question as to whether the chemical 

 heat regulation is independent of the muscular activity. In this case 

 we must differentiate between cold-blooded and warm-blooded animals. 

 In the first the metabolism rises with an increase in the surrounding 

 temperature, while in the second group the conditions are different. 

 The experiments of SPECK, LOEWY and JOHANSSON 4 on human beings 

 have shown that the lowering of the external temperature is without 

 influence upon the extent of metabolism (measured by the gas exchange) 

 only as long as all natural and non-voluntary movements of the muscles 

 are excluded. A chemical heat regulation, i.e., a rise in metabolism 

 without noticable movements of the muscles, is not accepted in man, 

 or at least it has not been proven. The heat regulation, in man, at lower 

 temperatures seems to be brought about by the natural or reflex pro- 

 duction of muscle action, nor has a chemical heat regulation in the 

 reverse sense, namely, a fall in the catabolism by raising the external 

 temperature, been shown in man. On the contrary in several cases a 

 small rise in the metabolism has been observed on raising the tem- 

 perature above the zone within which the fundamental catabolism of 

 the individual showed its minimum (Vorr, RUBNER 5 ). The investiga- 

 tions of EYKMAN 6 upon inhabitants of the tropics also show the same 

 result, namely, that in human beings no appreciable chemical heat regula- 

 tion occurs. 



In animals, a rise in the external temperature causes to a certain extent 



1 Rubner, Ludwig-Festschr., 1887; Loewy, Berl. klin. Wochenschr., 1891, 434; 

 Johansson, Skand. Arch. f. Physiol., &. 



2 Speck, 1. c.; Loeb, Pfliiger's Arch., 42; Ewald, Journ. of Physiol., 13. 



3 See larger handbooks for the literature on this question. 



4 Speck, 1. c.; Loewy, Pfliiger's Arch., 46; Johansson, Skand. Arch. f. Physiol., 7. 



5 C. Voit, Zeitschr. f. Biol., 14; Rubner, Arch. f. Hyg., 38. 



6 Virchow's Arch., 133, and Pfliiger's Arch., 64. 



