JANUARY 11, 1901.] 
means of which we can measure these 
changes in blood flow, and thus approxi- 
mately determine the intensity of mental 
activity under different conditions. I need 
not here describe the instrument any fur- 
ther than to say that it consists of an ap- 
paratus for measuring the volume of the 
hand or arm. When the brain is working 
actively the arm shrinks in size, the shrink- 
age being due to a shunting, so to speak, of 
some of its blood to the brain. I have had 
occasion to use this apparatus repeatedly 
in my laboratory, and the results seem to 
indicate quite clearly that an important 
factor in bringing about increased circula- 
tion through the brain, and therefore prob- 
ably an accompanying intensity of brain ac- 
tivity, is that of a high degree of interest in 
the subject of thought or discussion. 
I may be permitted to describe one or two 
incidents which, though trivial in them- 
selves, illustrate the point I am making. 
It happened on one occasion that a gradu- 
ate student in my laboratory, a Catholic 
priest, was using this apparatus in the 
course of some investigations upon the 
physiological effects of pleasant and un- 
pleasant sensations. 
problem he made a number of tests of the 
effect of strong mental activity upon the cir- 
culation. In one of these experiments he 
had a young theological student in the 
apparatus and was putting him through 
an examination, with the result that the 
record showed some indication of increased 
mental activity. He had arranged, how- 
ever, that while the experiment was in 
progress one of the young man’s regular 
teachers should appear suddenly upon the 
scene and pretend to give him his final 
examination which was due at about that 
time. The ruse succeeded admirably ; the 
student took the examination seriously and 
the effect upon his arm was so great that 
the apparatus was unable to record the 
full extent of its shrinkage. It was a capi- 
SCLENCE. 
In connection with his’ 
5d 
tal illustration of the effect on the circula- 
tory system of intense mental activity when 
accompanied by some degree of emotional 
excitement; or as a Methodist Bishop, to 
whom I was showing the record, expressed 
himself, it showed the serious effect that 
dogmatic theology may have on the ex- 
tremities. 
On another occasion, a colleague of the 
priest, who was himself an instructor in a 
theological seminary, was placed in the ap- 
paratus and subjected to an examination. 
The result upon his extremities was very 
slight. The truth was that he was on 
familiar grounds, he was as well acquainted 
with the subject as his interlocutor, and 
perhaps was a little weary of it. The ex- 
perimenter, however, recalled that his 
friend was from Kentucky and began to ask 
some questions concerning the blue-grass 
region, the breeds of race-horses and horses 
in general. He was delighted to find that 
he not only got an enthusiastic and minute 
description of the region and its famous 
racers, but, that his apparatus. gave most 
satisfactory indications that the sluggish 
brain had been fully aroused, and was 
working in its best form as regards the sub- 
ject under discussion. 
Many similar results obtained by other 
observers bear witness to the general truth 
that the element of interest is an important 
factor in stimulating brain activity, and so 
acting upon the vaso-motor centers as to 
put this organ under its most favorable 
physiological conditions for work. The 
brain that is but half aroused and interested 
is in fact partly unconscious. Much that 
it sees or hears fails utterly to awaken that 
chain of associations, that synthesis and 
comparison of memory records which forms 
the physical basis of mental growth and 
training. 
It is possible, I believe, that this factor 
is not entirely appreciated in our college 
teaching. Some weight, indeed consider- 
