FUNCTIONS OF THE BRAIN 949 



ence satisfaction when fed, become angry when attacked, see a very 

 bright light, avoid obstacles, hear loud sounds, such as those pro- 

 duced by a fog-horn, and can be awakened by them. They are not 

 completely deprived of sensations of taste and touch. But it ought 

 to be remembered that the interpretation of the objective signs of 

 sensation in animals is beset with difficulties; and although every- 

 body admits the accuracy of Goltz's description of what is to be 

 seen, his interpretation of the facts has been severely criticized, 

 particularly by H. Munk. 



Difficult as it is to keep dogs alive after removal of the greater 

 part of the cerebrum, the problem is far more difficult in monkeys. 

 In some recent experiments, however, in which the hemispheres 

 were removed by two successive operations from Macaque monkeys, 

 one of the animals survived for as long as twenty-six days the ex- 

 cision of the second hemisphere, and others lived a week. The 

 movements of the extremities were much affected. The animals 

 seemed to be in a sleepy condition with the eyelids closed, and most 

 of them made no movements which could be interpreted as voluntary 

 movements during the first days after loss of the second hemisphere. 

 Sounds caused the appropriate reflex movements of the ears. The 

 pupil was constricted by light. The animals cried in the usual 

 manner when subjected to painful stimuli, but the ordinary facial 

 accompaniments of pain were absent. 



In man the destruction of considerable masses of brain-substance, 

 particularly if gradual, is not necessarily fatal. How great a loss 

 is compatible with life cannot be exactly stated. It depends to a 

 large extent on the position of the lesion. But it is possible that 

 one cerebral hemisphere may be rendered functionally useless 

 without immediately putting a term to existence. In the foetus, 

 however, no portion of the great brain is absolutely indispensable for 

 life and movement. An anencephalous foetus (in which the brain has 

 remained undeveloped) may be born alive, and live for a short time. 



We see, then, that homologous organs are not necessarily, nor 

 indeed usually, of the same physiological value in different kinds of 

 animals. A loss which perhaps hardly narrows the range of the 

 psychical, and certainly restricts only to a slight extent the physical 

 powers of a fish, impairs in a marked degree the voluntary move- 

 ments of a dog, still more those of a monkey, in addition to cutting 

 off from it a great part of its intellectual life, and is in man incom- 

 patible with life altogether. It would be easy, however, to exag- 

 gerate the difference in the importance of the cerebrum to the higher 

 and the lower animals. After all, it remains a striking fact that 

 monkeys and dogs can live in the absence of the cerebral hemispheres, 

 and to the remnant of the central nervous system which enables such 

 highly organized animals to support life must still be regarded as a 

 very wonderful and complex mechanism. Perhaps, indeed, it is 

 not too much to say that the real lesson of these experiments on the 



