212 



THE HUMAN MOTOR 



Benedict and Carpenter, (*)and Atwater ( 2 ) used the calorimetric 

 chamber to measure the increase of calorific production of a man 

 performing difficult intellectual operations. They obtained an 

 excess of 1-32 cal. in three hours, about 4 per 1,000 exactly. The 

 details of the observations are as follows : 



" From the accumulated data of this series of experiments on 

 the effects of intellectual work and its metabolism, it was found 

 that the number of pulsations, as well as the temperature of the 

 body, was slightly increased, and that the increase of the quantity 

 of vaporised water was about 5%, that of the exhaled carbonic 

 gas 2%, that of the oxygen about 6%, and that of the heat pro- 

 duced 0-50%, all under conditions of sustained cerebral effort, 

 such as those of students during examinations. 



" We are very strongly of the opinion that the results obtained 

 in the course of these experiments do not indicate that the cerebral 

 effort exerts any positive influence on the metabolic activity. "( 3 ) 



Some unpublished experiments on the expenditure of oxygen 

 of students doing mental work have led to the same conclusion. 

 It can be stated that intellectual activity involves no correspond- 

 ing measurable energetic expenditure. 



In view of this small calorific expenditure, it is remarkable that 

 intellectual activity produces fatigue, an undeniable fatigue, 

 often more maiked than that of the muscles. We cannot indeed 

 numerically compute that activity, but it does not follow that 

 it cannot give rise to toxic wastes as in the working of muscles 

 (Mosso). Mental activity must entail a material exchange and 

 disassociation of various substances, generally phosphates, and 

 it would seem to have an influence on the fatigue of the nervous 

 terminations which make contact with the muscles, that is to say, 

 it makes work more troublesome and sometimes even painful. 



(*) Benedict and Carpenter (Bulletin, No. 208, p. 45-100, 1909). 

 ( a ) Atwater and Benedict (Bulletin, No. 136, p. 101 and 121). 

 (*j Benedict and Carpenter (Bulletin, No. 208, p. 100, 1909). 



