928 METABOLISM. 



KATZENSTEIN by the statement that during work two kinds of chemical 

 processes act side by side. The one depends upon the work which is 

 connected with the production of carbon dioxide, also in the absence 

 of free oxygen, while the other brings about the regeneration which takes 

 place by the taking up of oxygen. When these two chief kinds of chemical 

 processes make the same progress the respiratory quotient remains 

 unchanged during work; if by hard work the decomposition is increased 

 as compared with the regeneration, then a raising of the respiratory 

 quotient takes place. If, on the contrary, moderate work is continued 

 and performed in a way so that irregularities and occasional changes 

 in the circulation and respiration are excluded or are without importance, 

 then the respiratory quotient may correspondingly remain the same 

 during work as in rest. Its extent is thus determined in the first place 

 by the nutritive material at its disposal (ZUNTZ and his pupils) . 



The 4 theory of -LOEWY and ZUNTZ, that the raising of the respiratory quotient 

 during work is to be explained by an insufficient supply of oxygen, is opposed 

 by LAULANIE.! He has observed the reverse, namely, a diminution in the 

 respiratory quotient during continuous excessive work, and this is not reconcilable 

 with the above statements. He considers that sugar is the source of muscular 

 energy, and that the rise in the respiratory quotient is due to an increased combus- 

 tion of sugar. Its diminution, he explains, is caused by a re-formation of sugar 

 from fat which takes place at the same time and is accompanied by an increased 

 consumption of oxygen. 



* In sleep metabolism decreases as compared with that during waking 

 hours, and the most essential reason for this is the muscular inactivity 

 during sleep. The investigations of RUBNER upon a dog, and of JOHANS- 

 SON 2 upon human beings, teach us that if the muscular work is elim- 

 inated the metabolism during waMng 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, S 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. 4 



Mental activity does not seem to have any influence on metabolism 

 according to the means at hand for studying this influence. 



i Arch, de Physiol. (5), 8, 572. 



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

 Johansson, Skand. Arch. f. Physiol., 8. 



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

 4 See larger handbooks for the literature on this question. 



