780 THE MOTOR CORTICAL CENTERS OF THE CEREBRUM. 



right eyebrow often inhibits speech. Color-perception is abolished or disturbed 

 by applying the warm hands upon the eye or by stroking the opposite side of the 

 head. Stroking in a direction opposite to that in which stroking had previously 

 been practised gradually abolishes the rigidity of the members in sleep ; blowing 

 does this immediately. Insane persons are susceptible to hypnotism equally 

 with healthy persons. Disagreeable complications arise only if the practice be 

 overdone; if, for example, it be repeated daily for one or two weeks with the same 

 person, who then readily falls spontaneously into a state of hypnotism and cata- 

 lepsy. 



Hypnotic states can be induced also in animals. Hens (also after removal of 

 the cerebrum) assume a rigid position if an object be suddenly placed in front 

 of the eye, or a straw be placed over the beak, or a chalk line be drawn 

 in front of the head pressed upon the ground (Kircher's miraculous experiment, 

 1644). Birds, rabbits, frogs remain irresponsive when held for a time by gentle 

 pressure in a fixed position upon the back; crabs stand upon the top of the head, 

 as well as the tips of their claws. 



Hypnotism may be employed therapeutically in cases of color-blindness, in- 

 somnia, hysterical convulsions and emotional disturbances. Also the influence of 

 suggestion may be important, but great care is necessary in its employment. 



THE MOTOR CORTICAL CENTERS OF THE CEREBRUM. 



Fritsch and Hitzig, in 1870, discovered upon the surface of the con- 

 volutions of the cerebrum a number of circumscribed areas, electrical 

 stimulation of which causes movement in definite groups of muscles 

 on the opposite side of the body (Fig. 258, I, II). 



Method. To the exposed gyri of the cerebrum (dog, ape) two blunt unpolar- 

 izable electrodes are applied close together, and stimulation is practised by means 

 of closure, opening or alternation of a constant current, the strength of which 

 causes a distinct sensation at the tip of the tongue; or the induced current is 

 employed, the strength of which causes a readily tolerated irritation at the tip 

 of the tongue. Luciani observed movements appear in consequence of mechanical 

 stimulation by scraping. The cerebrum is wholly insensitive to painful ma- 

 nipulations. 



The regions of the cerebral cortex, stimulation of which causes char- 

 acteristic movements, must be considered as true centers, as is evident 

 from the fact that the latent period after irritation of the centers and the 

 duration of the muscular contraction are longer than if the subcortical 

 fibers passing from the centers into the depth are irritated. In favor 

 of this view, further, is the circumstance that the irritability of the areas 

 in question can be modified by stimulation of centripetal nerves. Prob- 

 ably it is these centers upon which the will operates in the execution of 

 intended movements, and for this reason they are designated psycho- 

 motor centers by Landois. The motor zone of the brain is shown to be 

 a center also from the presence of special, large pyramidal cells. 



There are animals that come into the world with completely developed motor 

 and sensory functions. In these the motor cortical centers of the new-born are 

 already irritable. In such animals, however, that are born with incomplete motor 

 and sensory functions either the irritability of the cortex is still wanting entirely, 

 so that only the deeper fibers of the corona radiata are irritable, or movements can- 

 not yet be induced separately, and they are at the same time slower and more 

 sluggish, with a longer latent period. Man may exhibit an analogous condition. 

 Deep narcosis, as well as apnea and asphyxia, abolish the irritability of the 

 :rs, while the subcortical conducting fibers retain their irritability. Inter- 

 ference with the blood-supply to the head gives rise to loss of irritability of the 

 cortical centers and of the conducting fibers passing from them. After restoration 

 ot the circulation in the brain the irritability returns. Small doses of narcotic 

 poisons of atropm, moderate loss of blood, increased blood-pressure in the brain 

 and slight inflammation increase the irritability, while more profound influences 

 the same kind abolish it, as does also direct application of cold or of cocain. 



