1875.] Rev. S. Haughton on the Law of Fatigue. 43 



the distress of the fatigue produced became intolerable, and the number 

 of times each weight was lifted was noted. The students were required 

 to count " one — two" in time to the beat of the pendulum, so as to prevent 

 them from counting the total number of lifts of the weight. Professor 

 Macalister assisted me in these experiments ; and one of us counted the 

 number of lifts, while the other compelled the experimenters to observe 

 the conditions of the experiment, which were : — 



1. To keep time with the pendulum. 



2. To raise the weight in the transverse plane. 



3. To supinate the hands. 



4. To abstain from all bending of the knees or spinal column. 



The last three conditions are essential, in order to confine the work 

 done strictly to the same muscles, which, in this case, are the acromial 

 deltoid and supraspinatus muscles, whose average weight in the living sub- 

 ject is about 5*5 oz. av. 



The experimenter must be carefully watched, in order to ensure the 

 observance of these conditions ; for he is impelled instinctively and uncon- 

 sciously, by pain, to bring in other muscular fibres to aid those which are 

 suffering from the constrained and regulated motion. If this be per- 

 mitted, the law of fatigue will appear to be violated ; for of the muscular 

 fibres actually employed in doing work, some are quite tired out and 

 others not ; whereas the law of fatigue applies only to groups of muscles 

 all of which are completely exhausted. 



For each experiment I chose twenty students at random, using alto- 

 gether about fifty different students ; and no individual was experimented 

 upon again until an interval of forty-eight hours had elapsed. The 

 object of this arrangement was to avoid the effects of " training." In my 

 first Table I give the mean result of twenty different students ; and in my 

 second Table I have selected one student, set aside for the purpose, and 

 experimented upon once a week, so as to prevent the influence of 

 " training." In all cases there were three well-marked stages : — 



1. The work done with ease. 



2. Accompanied by respiratory distress. 



3. Accompanied by pain in the muscles used. 



During the last stage great care must be taken to prevent changes in 

 the posture and mode of motion, by which additional muscular fibres 

 may come in aid of the fibres nearly fatigued. 



Let "W denote the total work done, and T the time of doing it ; then, 

 by the law of fatigue, 



W 2 



___ = constant (1) 



If w be the weight held in the hand, and a be half the weight of the 

 arm, and n the number of times the weights are lifted ; since the time of 



