586 NERVOUS SYSTEM 



that some psychologists have regarded the human intelligence as distinct 

 in nature as well as in degree. Although physiologists do not commonly 

 accept this proposition, regarding the intelligence of man as simply su- 

 perior in degree to that of the lower animals, it is evident that this dif- 

 ference in the degree of development is so great as to render the human 

 mind hardly comparable with the intellectual attributes of animals low 

 in the scale. Still, there can be no doubt in regard to the identity of 

 the nature of the faculties of the brain in man and in some of the lower 

 animals, however much these faculties may differ in their development. 

 If this proposition be true, it is reasonable to apply experiments on 

 the brain in the lower animals to the physiology of corresponding parts 

 in the human subject. 



Extirpation of the Cerebrum. Experiments on different classes of 

 animals show clearly that the brain is less important, as regards the 

 ordinary manifestations of animal life, in proportion as its relative 

 development is smaller. For example, if the cerebral hemispheres are 

 removed from fishes or reptiles, the movements that are called voluntary 

 may be but little affected ; while if the same mutilation is performed in 

 birds or certain of the mammalia, the diminished power of voluntary 

 motion is much more marked. It would be plainly unphilosophical to 

 assume, because a fish or a frog will swim in water and execute move- 

 ments after removal of the hemispheres very like those of the uninjured 

 animal, that their feeble intelligence is not destroyed by the operation. 

 It is not only possible but probable that in the very lowest of the 

 vertebrates, the operations of the nervous centres are not the same as 

 in higher animals. There is, for example, a fish (the lancet-fish, amphi- 

 oxus lanceolatus) that has no brain, all the functions of animal life 

 being regulated by the gray substance of the spinal cord. It is 

 essential, therefore, in endeavoring to apply the results of experiments 

 on the brain in the lower animals to human physiology, to separate, so 

 far as possible, distinct manifestations of intelligence from automatic 

 acts. 



Flourens (1822 and 1823) made a series of observations on the 

 different parts of the encephalon. As regards the cerebral hemispheres, 

 he found that complete removal of these parts in living animals (frogs, 

 pigeons, fowls, mice, moles, cats and dogs) was invariably followed by 

 stupor, apparent loss of intelligence and absence of even the ordinary 

 instinctive acts. Animals thus mutilated retained general sensibility 

 and the power of voluntary movements, but were thought to be deprived 

 of the special senses of sight, hearing, smell and taste. As regards 

 general sensibility and voluntary movements, Flourens was of the opin- 

 ion that animals deprived of their cerebral lobes possessed sensation 



