77 6 



PSYCHIC FUNCTIONS OF THE CEREBRUM. 



accompanies paralysis of the external ocular muscles. In human beings with 

 impaired cutaneous sensibility, the eyes constitute the main dependence for the 

 maintenance of the equilibrium. Such individuals fall on closing the eyes. 



The frog with its cerebrum extirpated maintains the harmonious equilibrium 

 of its body. Placed upon its back, it at once rolls over; irritated, it makes one 

 or two jumps; thrown into the water, it swims to the margin of the reservoir, 

 climbs upon this and remains quietly seated. Under the most complex inciting 

 conditions it exhibits complete control, harmony and uniformity of its move- 

 ments. Without external irritation, however, it makes, at least at first, no inde- 

 pendent voluntary, purposeful movement. On the contrary,' it sits constantly 

 in the same place as if asleep, it takes no food, it has no conscious sense of hun- 

 ger or thirst, it exhibits no fear and, finally, it dries into a mummy. 



The pigeon behaves in the same way when its cerebral hemispheres are re- 

 moved. Unirritated, it remains seated as if in sleep, although if stimulated it 

 exhibits complete coordination in all movements in walking, flying, perching, 

 and balancing of the body. In the course of several days it changes its position 

 apparently without external excitation. The sensory nerves and those of special 

 sense, it is true, still conduct impulses to the brain, but these are capable of ex- 

 citing only reflex movements, and are no longer capable of exciting conscious 

 sensations. Therefore, the bird starts when a firearm is discharged in its vicinity, 

 its eyes blink when a flame is brought near- them and the pupils contract, it turns 

 its head when the vapor of ammonia is applied to its nose. All of these stimuli, 

 however, are not appreciated consciously as such. Conception, will, memory are 

 lost, and the animal spontaneously takes neither food nor drink. If these are 

 placed in the pharynx the animal swallows, and in such a manner its life may 

 be preserved for months. 



Fish behave somewhat differently. A carp whose cerebrum has been extir- 

 pated is capable of seeing and even of selecting its food and of moving voluntarily. 

 Under these circumstances the psychic function must be located also in the optic 

 thalamus. According to Schrader the frog is said in the further course of ob- 

 servation to behave in a similar manner. Reptiles also are able later to move 

 spontaneously, although they exhibit neither fear nor anger. Birds also are said 

 later on to exhibit spontaneous movement. Their organs of special sense func- 

 tionate, but they are mind-blind, mind-deaf, etc. 



Mammals. Goltz was able to remove the cerebrum from dogs and to keep 

 the animals alive for a long time. Subsequently they exhibited good powers of 

 locomotion and the ability to take food, as well as taste, tactile sensibility, hearing 

 and muscular sensibility. They were sensitive to bright light, without, how- 

 ever, being actually able to see. In other respects the dogs were in a state of 

 most profound dementia. Feeding alone affected them agreeably and they showed 

 also a sense of satiety. In other respects the loss was evident of all those mani- 

 festations from which conclusions are formed as to the existence of intelligence, 

 memory and judgment. 



Observations on somnambulists show that also in man complete 

 coordination of all movements may be present without the aid of con- 

 scious volition or conscious sensation and perception. Most ordinary 

 movements in the waking state, however, take place without the aid of 

 consciousness, being controlled from the midbrain. 



The degree of development of the mental activities in the animal kingdom varies 

 in accordance with the size of the cerebral hemispheres in proportion to the re- 

 maining portions of the central nervous system. If, however, the brain alone 

 is taken into consideration it will be found that those animals possess the higher 

 grade of intelligence in which the cerebral hemispheres greatly preponderate over 

 the midbrain. The latter is represented in the lower vertebrates by the optic 

 lobes, in the higher by the quadrigeminate bodies. In Fig. 258, VI represents 

 the brain of the carp, V that of the frog, IV that of the pigeon. In all of these 

 figures the hemispheres are indicated by the numeral i, the optic lobes by the 

 numeral 2, the cerebellum by the numeral 3 and the medulla oblongata by the 

 numeral 4. In carps the cerebrum is even smaller than the optic thalami, while 

 in frogs it is already larger than the latter. In pigeons the cerebrum extends 

 downward to the cerebellum. In correspondence with these variations in size is the 

 degree of intelligence present in the animals named. In the dog's brain (Fig. 2 58, II) 



