If the brains of dogs or monkeys, or other animals, are stimulated electrically, well-defined movements are produced in some part of the body; for example, in the face, tail, fore-leg, hind-leg, according to the portion of the brain stimulated. Moreover, the movements produced are on the opposite side of the body. All experiments confirm the belief that each hemisphere of the brain controls functions on the opposite side of the body. The crossing of nerves in the medulla indicates the same fact.

If a portion of the brain is excised or destroyed, the corresponding functions will be inhibited or destroyed. Paralysis of various

FIG. 19.-Mesial surface of the human brain, showing several localized areas. (Drawn by Call.)

organs results from disturbance of certain portions of the nervous system. The disturbance may be caused by pressure or degeneration. In many cases caused by pressure, physicians are able to diagnose accurately and afford relief by cutting into the skull and relieving the pressure. Trephining to relieve paralyIsis is now very common. Halleck cites two cases. The first was that of an epileptic patient in whom all the preliminary twitchings began in the left shoulder. "The surgeons cut a circular hole immediately over the shoulder centre. Beneath the incision they found a small tumor, which they removed." The second case was that of a sewing-girl in whom all the pre

liminary convulsions began in the right thumb. "The surgeons cut through the skull directly over the motor centre for the hand. Then they stimulated the brain cortex until they found a surface where the thumb alone was flexed. It was necessary to determine this point accurately, for if the brain beyond this was injured, the hand and entire arm would be paralyzed. . . . The surgeons succeeded in removing the thumb centre alone, and, as a result of the operation, her epileptic attacks were fewer and milder in number. She also had the use of her hand." 1

Of the wonderful accuracy and progress in localizing brain areas, Dr. Keen wrote: "When I say that the existence of a tumor about the size of the end of the forefinger can be diagnosticated, and that before touching the head it should be said that it was a small tumor, that it did not lie on the surface of the brain, but a little underneath it, that it lay partly under the centre for the face and partly under that for the arm in the left side of the brain, and that the man was operated on, and the tumor found exactly where it was believed to be, with perfect recovery of the patient, it is something which ten years ago would have been deemed the art of a magician rather than the cold precision of science."

Localization of Brain Not Exceptional.-There is nothing strange in the fact of localization of function in the brain, although some people are incredulous concerning it. No one regards it as strange that the body is divided into head, trunk, arms, legs, hands, heart, liver, and spleen, each subserving a specific function which no other organ can perform. It is accepted as a matter of course that the eye cannot hear, the ear see, or the hand taste. Even the division of the nervous system into brain and nerves excites no comment. But as soon as specialization of function in the various portions of the brain is mentioned, doubts begin to arise. Of course, the different parts are related-sometimes very closely indeed. So also are the ear and the œsophagus, both having arisen from the same

1 Education of the Central Nervous System, p. 15.

Vivisection and Brain Surgery.

original tissue. The linings of the of the body are the same in origin.

stomach and the outer skin

Traced to their origins we

find that the brain, muscles, bones, skin, hair, and in fact all

p. 267.)

logical basis for evolving (After Starr, from Donaldson's Growth of the Brain, idealistic philosophy or writing poetry. A dog and a man may subsist on an identical quality and quantity of food, but how different the resultants!

The facts revealed by an examination of the brain of Laura Bridgman were very significant. She was in possession of all her senses until three years old, when scarlet fever deprived her of the sight of the left eye. She could see a little with her right eye until eight, when she became entirely blind. From three years of age she was stone-deaf. Consequently she was devoid of experiences to awaken the areas of sight and hearing. It was found that those areas of the brain were much less well developed than the corresponding areas of normal brains or the other areas of her own brain. Dr. Donaldson, who made the examination of the brain with such minute care, said: "In this connection it is interesting to notice that those parts of the cortex which, according to the current view, were to be associated with the defective 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 nerve cells smaller, but the impression made on the observer was that they were less numerous than in the normal cortex." As we now might expect,

he found the right side of the cortex in the occipital region much thinner than the left side. Undoubtedly the earlier blindness of the left eye caused the earlier arrest or atrophy of the left side of the visual centre, and the experiences in seeing with the right eye, even though poorly, for a few years, caused the superior development of the centre controlling that eye.1

Association Tracts a Form of Localization.-Another type of brain specialization and localization of much interest and importance educationally is found in the special mechanisms for association. These are the association fibres (a) connecting the adjacent convolutions; (b) those connecting different tracts, especially those connecting the frontal and occipital, and the frontal and temporal areas; and (c) those connecting sensory and motor areas (see Fig. 20). The commissural fibres connecting the two hemispheres are in reality association fibres securing harmony between the actions of the two halves of the brain.

The groups of association fibres connecting the various convolutions are so definite as to be readily seen with the naked eye, as are those between the larger lobes. These are all well established by heredity and only await proper stimulation to develop fully. That they need proper exercise is shown by the facts that at birth they are undeveloped and they develop best in those with normal experiences. In the feeble-minded they are poorly developed.

Obscure Association Tracts.-But there are other association paths not so easy of observation; in fact, most of what we know of them is through the observed data of nervous anatomy and the well-tested data on the transmission of nervous energy, and through our knowledge of functional relations established. While we cannot always see the relations by a study of anatomical structure, we can observe the behavior through expression. Just as we know that every impression must result in some motor expression, we are also sure that every series of muscular and psychic connections is the consequent of nervous connections

'Donaldson, On the Brain of Laura Bridgman, Am. Jour. of Psych., Sept., 1890, Dec., 1891.

established. Any set of sensory cells may become connected with any other sensory cells or any other motor cells. We know that we connect visual impressions with other visual impressions, and also with sounds,

tastes, and smells, and with a variety of motor activities. Because of these psychic relations and because of the knowledge of psycho-physical parallelism we know that neural connections are established, though not possible to be seen. In fact, the brain, as suggested before, is a wonderful co-ordinating machine. The greater the

FIG. 21.-Projection fibres of the human brain.

(After Starr, from Donaldson's Growth of the Brain, p. 256.) Note how all the tracts of projecting fibres have their origin in the original stem of the nervous system. They represent specialized portions and go to still other specialized portions.

complexity of co-ordinations and the finer their adjustments, the higher the type of brain and the higher the type of intelligence of its possessor. Contrast the brains and activities of a reptile with those of man, who can play a piano, make a watch, construct an engine, or paint a picture.

Undoubtedly a caution should be given against thinking that all functions can be localized or that each portion of the brain can be demonstrated to control a particular function. Specialists in anatomy and physiology are particularly cautious in their statements on this matter. A good many facts have been definitely established and much progress is being made.1 Undoubtedly each complex action functions in many centres, and also without doubt each centre functions in many kinds of actions. The association tracts connecting the various centres are probably much more specialized and limited in their functions than are the centres. May we not compare the centres to

1See Howell, Text-Book of Physiology, chap. IX; Church and Peterson, Nervous and Mental Diseases, pp. 161-180; and other medical works.