1911-12.] A Method of Measuring Mental Processes. 
73 
X. — A Method of Measuring Mental Processes in Normal and 
Insane People, with special reference to Maniac Depressive 
Insanity. By George Rutherford Jeffrey, M.D. (Glasg.), F.R.C.P. 
(Edin.), Senior Assistant Physician, Crichton Royal Institution, 
Dumfries ; late Senior Assistant Physician, District Asylum, Ayr. 
Communicated by Sir James Crichton-Browne. 
(MS. received September 5, 1911. Read November 13, 1911.) 
Among the problems which confront the psychiatrist in arriving at a 
judgment upon a mental case, few are more difficult than the estimation 
of the patient’s mental working capacity. A rough approximation may 
be attained by careful observation of the patient’s daily reaction to his 
surroundings — by the attitude he adopts to the little problems of his daily 
life; but such is, at best, only a very vague and unsatisfactory measure. 
To impose simple tasks for the purpose of obtaining objective criteria upon 
which to base our judgment is unusually difficult, and patients who were 
incapable of comprehending the new task would have to be excluded from 
its action ; and to interest the patients in such a task sufficiently to persuade 
them to do their best is often not possible. The estimation of the working 
capacity of a large proportion of patients would thus seem at first sight to 
he beyond our powers to ascertain. 
Hence it is that the methods adopted by psychologists for ascertaining 
the mental working capacity in normal life have generally been found 
unpractical in insanity. 
Kraepelin and his followers, in their investigations of tea, coffee, ethyl 
alcohol, amyl alcohol, bromides, and other medicinal substances, have, 
however, used a method which in their hands seems to have proved 
eminently satisfactory, not only for normal but also for abnormal mental 
states. Their test has recently been fully described (1), so I need here only 
briefly refer to its essential features. In it the question of the compre- 
hension of a new mental task by the patient has been solved by utilising 
as the basis for the test one of the most primitive and familiar of our 
everyday experiences — the act of simple addition. The test consists of the 
addition of digits in pairs as rapidly as possible. The figures from 1 to 
9 are systematically arranged, so that as far as possible the difficulty of 
adding each single pair is constant. Each pair, therefore, is taken to 
represent a constant unit of mental work, and the test enables not only 
the number of units of mental work done throughout a given period — 
