280 



72 



certain work than somebody else, it will naturally give him less trouble and con- 

 sequently involve smaller changes of metabolism. 



When the subject for some reason or other feels indisposed and must exert 

 himself to a great extent in order to carry through what he is wanted to, the me- 

 tabolism will, as a rule, show a considerable increase besides that, which asserts it- 

 self under normal conditions. On the other hand if the subject finds the work very 

 easy for some reason or other, so that it may be carried through with ease, or if 

 the mental work is altogether lo be regarded as recreation and rest, then the meta- 

 bolism can be reduced to such an extent that the increase is negative on an average. 

 — These deviations from the normal changes of metabolism during mental work get 

 explained by the fact, that a strain or relaxation of the attention will involve cor- 

 responding changes of the muscular tone, through which the metabolism is increased 

 or decreased. 



The changes of the muscular tone, which accompany the strain of attention, 

 are under normal conditions limited probably to the muscles of the head, the arms 

 and the hands, where their strength will grow with the concentration. 



Emotions and sentiments will also cause tensions of the muscles, which may 

 appear in all the muscles of the body, varying altogether in extensity and intensity 

 with the kind of emotion in question. The difference between an emotion and the 

 corresponding esthetic sentiment seems especially to depend upon the varying in- 

 tensity with which the tension of the muscles appears during the two conditions. 



The metabolism during the rest-period after the work is on an average less 

 pronounced than during the rest-period before the work. Such a change af level 

 seems only to appear during work, whereas only a slight oscillation of metabolism 

 is perceptible during entire rest. The change of level depends in all likelihood upon 

 a gradually appearing relaxation of the tone of the body-muscles, created by the 

 inhibition of the work, that is to say, the psycho-physiological processes on the 

 latent innervation of the muscles. 



The decrease of the rest-metabolism during work will be counteracted when 

 external or internal disturbances involve an intense strain of attention, which will 

 invariably result in a considerable increase of muscular tone. The rest-metabolism 

 may in such cases be bigger after the work than before. 



When owing to its facility the work involves a relaxation of attention, the 

 immediate result will be a voluntary relaxation of the body-muscles, which is again 

 followed by the metabolic increases being negative in the beginning. 



The greatly reduced muscular tone seems however incompatible with continued 

 activity, and the metabolic increases will consequently become positive again sooner 

 or later. 



The increases of CO^ during mental work are only slightly due lo a dilution 

 of COg, even if this may to a certain extent be accountable for the CO^ values ob- 

 tained varying more than the corresponding 0.^ values. 



If a mental work is so easy or short that the sensation of fatigue is not felt, 



