THE LAWS OF ENERGETIC EXPENDITURE 175 



speed at which work is done ; they have also shown that the 

 expenditure, however great it may be, has a minimum value for 

 certain conditions of load or effort. According to Treves' experi- 

 ments in Italy, on the flexors of the forearm, the determining 

 cause of the effort, is found in the resistance to be overcome or 

 the load to be displaced. It is the sense of resistance which 

 regulates the functioning of the muscles^ 1 ) that is to say, the 

 motor nervous excitation. We have seen that the nervous 

 excitation necessitates an expenditure of energy of not less than 

 2-5% of the expenditure of static effort ( 116). Nervous excita- 

 tion is costly, and must not be abused. Voluntary work, which 

 reduces the effort to a minimum, regulates and conserves also the 

 nervous intervention. 



One characteristic of voluntary work is that it is always 

 accomplished with minimum expenditure. The load to be dis- 

 placed, or the corresponding effort, the speed, and the time must 

 have certain very definite values to obtain an economical maxi- 

 mum. Muscular action is periodic ( 90) on account of fatigue. 

 Hence the absolute maximum can only relate to a definite period 

 of time, or a succession of periods separated by intervals of repose. ] 



These results, so valuable to industry, were obtained by means 

 of the " ergograph " (from epyov, work), of which the first type 

 was invented by Mosso (see Technics, 222). The principle of 

 the ergograph consists in opposing a resistance (a weight P) to 

 the muscles, and recording the contractions graphically. 



Fio. 133 

 Types of Ergograms. 



If h is the vertical height of the trace of a muscular contraction 

 and P the weight, the work done in one contraction = Ph. If, 



(!) TrSves (Arch. ital. de Biologie, vol. xxx., pp. 1 & 11 ; 1898), 



