METABOLISM AND WORK. 869 



The quantity of carbon dioxide eliminated during a working period 

 is uniformly greater than the quantity of oxygen taken up at the same 

 time, and hence a raising of the respiratory quotient was usually con- 

 sidered as caused by work. This rise does not seem to be based upon the 

 character of chemical processes going on during work, as we have a series 

 of experiments made by ZUNTZ and his collaborators, LEHMANN, KAT- 

 ZEXSTEIN and HAGEMANN, 1 in which the respiratory quotient remained 

 almost wholly unchanged in spite of work. According to LoEWY 2 the 

 combustion processes in the animal body go on in the same way in work 

 as in rest, and a raising of the respiratory quotient (irrespective of the 

 transient change in the respiratory mechanism) takes place only with 

 insufficient supply of oxygen to the muscles, as in continuous fatiguing 

 work or excessive muscular activity for a brief period, also with local 

 lack of oxygen caused by excessive work of certain groups of muscles. 

 This varying condition of the respiratory quotient has been explained by 

 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 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. 3 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- 



1 See footnote 2, page 868. 2 Pfliiger's Arch., 49. 3 Arch, de Physiol. (5), 8, 572. 



