THE QUESTION OP FATIGUE FROM THE ECONOMIC STANDPOINT. 301 



' time-distribution ' curve of accidents, yet such accidents form a small 

 proportion of all accidents, varying for different industries, but not 

 likely to exceed 20 per cent. 



The exact psycho-physiological modus operandi by which the tests 

 I shall mainly use, i.e., the output of work and the occurrence of 

 accidents, may be expected to vary with fatigue (output inversely and 

 accidents congruently) has been explained by Dr. Imberfc, of Mont- 

 pellier University, in a paper to the Congress of Demography and 

 Social Hygiene held at Brussels in 1903 : 



' A result of the slowing down and decrease in the rapidity of the 

 muscular contraction ' (a physiological characteristic of fatigue) ' is that 

 the speed of work, that is to say the quantity of work performed during 

 a unit of time, will diminish as the expenditure of energy increases 

 and fatigue becomes more intense. It follows that an estimate 

 (Vappriciation) if not the exact measure of the speed of work should 

 provide a method (procMS) and often a very simple one of discovering 

 the existence of fatigue. 



' The occurrence of which an accident is the result sometimes takes 

 place with such suddenness that the worker may fall a victim at the 

 very moment when he perceives the danger that threatens him or even 

 before he sees that danger. In other cases on the contrary, the occur- 

 rence is less sudden, and the workman sees it coming and can often 

 escape it {s'y soustraire) by a few rapid and energetic movements of 

 retreat or protection. But it is then a question of making use of a 

 movement which may not be more than a fraction of a second, and 

 one may imagine from this how fatal the action of fatigue on the rapidity 

 of muscular contractions and relaxation (reldchemeni) may be for the 

 workman affected. 



' Moreover, to estimate with a full knowledge of the causes the ability 

 (aptitude) of a worker to save himself from a danger that threatens him 

 unexpectedly (inopindment), one must consider the phenomena of 

 fatigue other than those of jihysical fatigue. The conscious perception 

 of danger, indeed the realisation of those voluntary movements which 

 can save us, is a complex act taking its origin in a peripheric excite- 

 ment (visual, auditive, &c.) and its end in muscular contractions after 

 intermediate cerebral operations. . . . From already numerous experi- 

 ments it is found that we can measure the duration of such a complex 

 phenomenon and that such duration is far from being negligible in 

 regard to the question here considered, and that further the duration is 

 influenced by certain circumstances. By experiments it has been 

 established tlaat for a whole act relatively simple the total reaction time 

 is notably longer when the organism is in a state of physical fatigue. ' 



These quotations from Imbert suggest that while the output-rate is 

 largely affected by fatigue directly, by the very diminution of speed, the 

 accident rate, on the other hand, is affected through the channel of 

 decreased ' nervous ' activity in attention, sensitivity, and speed o? 

 reaction to which Bogardus would certainly add the channel of less 

 active muscular control. How far the output rate is also affected thus 

 indirectly would depend on the nature of the work, and especially the 

 nervous activities involved (see Section I. a), and channels through 



