206 THE HUMAN MOTOR 



free energy transformable into mechanical work. At the same 

 time it maintains the temperature of the body at about 37 C 

 because this is a necessity. This expenditure in regulation 

 appears to be at the expense of the fats in preference to all other 

 alimentary substances ( 110). 



The activity of the muscles increases the activity of the 

 humoral circulation^ 1 ) (blood and lymph) provokes a speed of 

 bodily combustion which can raise the general temperature by 

 about 1C ( 2 ) ( 105), and assists the digestive functions to an 

 appreciable extent. 



Even the nervous centres profit by this general movement of 

 the internal life as is shewn by their accentuated responsiveness 

 to the rapidity of sensations or actions. It has been recognised, 

 for instance, that the tactile sensibility is increased and rendered 

 more delicate, notably in the case of typographers. 



Men who devote much time exclusively to brain work feel the 

 need of stimulating, by means of physical work, the nervous 

 system, the respiratory organs, and the muscular power, which 

 is almost suspended during the period of concentrated thought. 



Any person who has the aptitude for work is fit to succeed in 

 all professions or occupations because his muscles and his nerves 

 are disciplined for this manifold end. Physiologcially, work 

 breeds the aptitude for work. 



146. The Limits of Work : Fatigue. Fatigue can be defined 

 as the effect which limits the duration of work. In the case of 

 inanimate motors, owing to molecular alterations of a physical 

 order, fatigue attacks all parts subjected to stresses, though very 

 slowly. In the case of living motors, man and animals, the fatigue 

 either decreases the intensity of the muscular effort, or reduces 

 the contraction of the muscle. This will be further explained 

 later. The result of fatigue is a lessened aptitude for work. The 

 ergographic tracing ( 119) shows this decrease in the quantity 

 of work done by contraction. As already shown, the curve will 

 descend quicker or slower according to the rhythm of the con- 

 tractions and the intensity of the effort. It must be noted, as 

 Imbert showed, that the real muscular fatigue is slow, although it 

 is shown very quickly on the ergograph in consequence of the 

 sensation of pain.( 3 ) The conditions of the ergographic work 

 of the finger generally cause discomfort and the traces in fig. 142 

 show this discomfort lather than the real fatigue of the flexor 

 muscles. 



(*) Mossu (Comptes Rendus Diologia, 1900). 



( a ) Forel (Revue Scient., 1885) ; Marcet (Archives Sc. Nat, de Geneva, 

 1885) ; Woodhead (Journal of Physiol., vol. xxiii., 1898-99) ; Atwater 

 and Snell (loc. cit.). 



( 8 ) A. Imbert (Comptes Rendus A cad. Sciences, 31st October, 1910.) 



