114 
PSYCHOLOGY: R. M. YERKES 
directions is obvious. It must depend on the gradient of chemical 
activity along the fiber, and the amount of increase of this activity at 
the point of stimulation. 
I believe the nerve impulse is a propagation of chemical change — the 
propagation being due to a restoration of an equihbrium disturbed by 
the increase of metabolism at the point of stimulus. This propagation 
is always toward the point where there is less chemical activity, as 
measured by carbon dioxide production. 
1 Amer. J. Physiol., 35, 340. 
A POINT SCALE FOR MEASURING MENTAL ABILITY 
By Robert M. Yerkes 
PSYCHOPATHIC DEPARTMENT, BOSTON STATE HOSPITAL 
Presented to the Academy, December 4, 1914 
Alfred Binet, in 1905, devised a method of roughly estimating the 
intellectual capacity, or degree of mental development, of the child in 
terms of age. The method depended upon the application of series of 
single tests or measures, each series being especially arranged for a 
particular year of age. If a subject could satisfactorily meet the require- 
ments for his age, he was considered up to the standard. Obviously 
he might measure either a certain number of years above or below the 
expected intellectual age. 
The Binet measuring scale of intelHgence has been revised, perfected, 
and adapted by various individuals, and now after nearly ten years 
of practical application, it stands as the only convenient and reason- 
ably expeditious method of classifying children with respect to intelli- 
gence. It possesses, however, many serious defects which may not now 
be enumerated, since the purpose of this abstract is to present a brief 
description of a new method which is based, on the one hand upon the 
work of Binet and his associates, and on the other upon a suggestion 
made by the late E. B. Huey. We may call this new method the point 
scale for measuring mental capacity. It has been developed at the 
Psychopathic Hospital, Boston, as one result of the demand for rea- 
sonably detailed and rehable information concerning the mental char- 
acteristics of individuals both immature and mature. The scale con- 
sists of a single series of measurements to be made on all subjects. Each 
measurement is evaluated according to a graded scale, and the maxi- 
mum credit obtainable in an examination is one hundred points. The 
