g else which serves as proper
stimulus to the sense organs, and to every form of intellectual and
social interest; and (2) no less important, an opportunity for the
freest and most complete forms of response and motor activity.

[Illustration: FIG. 15.--Schematic transverse section of the human brain
showing the projection of the motor fibers, their crossing in the
neighborhood of the medulla, and their termination in the different
areas of localized function in the cortex. S, fissure of Sylvius; M, the
medulla; VII, the roots of the facial nerves.]

An illustration of the effects of the lack of sensory stimuli on the
cortex is well shown in the case of Laura Bridgman, whose brain was
studied by Professor Donaldson after her death. Laura Bridgman was born
a normal child, and developed as other children do up to the age of
nearly three years. At this time, through an attack of scarlet fever,
she lost her hearing completely and also the sight of her left eye. Her
right eye was so badly affected that she could see but little; and it,
too, became entirely blind when she was eight. She lived in this
condition until she was sixty years old, when she died. Professor
Donaldson submitted the cortex of her brain to a most careful
examination, also comparing the corresponding areas on the two
hemispheres with each other. He found that as a whole the cortex was
thinner than in the case of normal individuals. He found also that the
cortical area connected with the left eye--namely, the right occipital
region--was much thinner than that for the right eye, which had retained
its sight longer than the other. He says: "It is interesting to notice
that those parts of the cortex which, according to the current view,
were associated with the defective sense organs were also particularly
thin. The cause of this thinness was found to be due, at least in part,
to the small size of the nerve cells there present. Not only were the
large and medium-sized cells smaller, but the impression made on the
observer was that they were also less numerous than in the normal
cortex."

EFFECT OF SENSORY STIMULI.--No doubt if we could examine the brain of a
person who has grown up in an environment rich in stimuli to the eye,
where nature, earth, and sky have presented a changing panorama of color
and form to attract the eye; where all the sounds of nature, from the
chirp of the insect to the roar of the waves and the murmur of the
breeze, and from the so