568 THE POPULAR SCIENCE MONTHLY 



COMMON FACTOKS IN MENTAL HEALTH AND ILLNESS 



Br Dr. P. LYMAN WELLS 



MCLEAN HOSPITAL 



Denn sie hatte, — wie die meisten Menschen, — nur die Wahl zwisehen Tobsucht 

 und Ergebenheit. — Simplicissimus, 18, 661. 



AM asked to deal in these remarks with variations in different 

 J- human traits which are produced by pathological conditions. 

 For example, although in health John's eyesight is sometimes better or 

 worse than at others, yet John's eyesight is so consistently better than 

 James's that we speak of John as having better eyesight than James. 

 But John's eyesight might become much worse as the result of a central 

 lesion, and, if it remained fairly stationary at its new level, John would 

 have much worse eyesight than James as the result of the pathological 

 condition, and a new individual difference would be produced. The 

 psychoses of which we shall speak, however, do not act in altogether this 

 way. The differences associated with them are not sufficiently stable 

 at any one level to make it just to say, e. g., that a general paralytic has 

 on the average one half the memory capacity of the normal. We can 

 therefore speak of the kind, direction and limits of such changes, but 

 not of their amount as representative of any clinical group. 



It is one of the gentle ironies of scientific history that the concept of 

 individual differences should have originated with one of its least sig- 

 nificant functions. One must needs be the assistant of a pre-Galtonian 

 astronomer to suffer for his simple reaction time. This fact, together 

 with the necessary technical complications, has not encouraged the ac- 

 cumulation of pathological data on the " personal equation." The most 

 important determinations are those of Diefendorf and Dodge, on the 

 reaction time of the eye-movements. They found lengthened time in 

 all the psychoses tested, slightest in the manic-depressive excitements 

 and in dementia prcecox, most marked, as would be expected, in manic- 

 depressive depression. The angular velocity of eye-movements was 

 found by these authors to be somewhat more rapid than normal in 

 dementia prcecox, general paralysis, and slightly also in manic-depress- 

 ive excitement, while the slowest movements were seen in the depressions 

 and in epilepsy. The generally quick movements of manic cases and 

 the slowness of depressed ones are a clinical commonplace. 



The rapidity with which some small movements can be repeated has 

 a special neurological meaning, and many observations have been made 

 with the psychoses. The rate is probably a little faster than the normal 



