84 
Proceedings of the Royal Society of Edinburgh. [Sess. 
fatigue was slowly becoming more evident ; it was combatted successfully 
for two minutes during which the rate remained at a constant and almost 
average level ; and then the output precipitately diminished : even in the 
fatigue, the maximum capacity for that state was yielded, for A was 
incapable of summoning up energy even for the end spurt. Here, the 
Hylan middle period gave a good estimate of the mental working capacity, 
and it was certainly a period without variations. 
Very different was the curve of B’s (H in tables) average work from 
minute to minute during the second five days. The rate was in no two 
successive minutes uniform. The initial and terminal spurts were dis- 
tinguishable ; but between them the curve resembled a series of saw teeth. 
The average of the middle five-minute period was below the true average 
working capacity, and this middle period was at least as variable in its 
output as any other. 
The mental work of a person in a given period appears to be 
characteristically represented by no part of that period. The output at the 
beginning and at the end are characteristic only of the part of the period 
in which it is produced. The average output, the average mental working 
capacity, is most closely represented by the arithmetical mean of the 
whole test. 
In the cases of maniac depressive insanity, the age of the patients 
varied greatly ; their previous familiarity with figures was unequal ; for 
some had been professional men, some tradesmen, some had been engaged 
in household duties, and others had never had any definite employment ; 
and some were excited, some depressed, and others were apparently 
enjoying a normal interval. As regards the amount of their mental 
working capacity, no harmony was therefore to be expected. 
Total Output. 
Of the thirty cases examined, the work done on the first day varied 
from 81 to 739 units. Case 10 was the only one whose initial output was 
below 100. Seven cases did less than 200 units ; thirteen less than 300 ; 
nineteen less than 400 ; twenty-six less than 500 ; and twenty-nine less 
than 600. The average output on the first day was 339, i.e. 389 (53 per 
cent.) below the normal. 
Three cases were in a state of excitement (Cases 18, 22, 28). Their 
maximum output was 400, 605 and 309 respectively : their maximum 
mental working capacity therefore averaged 438, and was 60 ’4 per cent, 
below the normal average. 
