6 96 NERVOUS SYSTEM. 



physiological inquiry in which it is so difficult to apply experiments upon the inferior ani- 

 mals to the human suhject, and none in which the results of experiments should be 

 received with greater caution. The reason for this is Apparent enough. The brain and 

 the intellectual power of man are so far superior to the development of this organ and 

 its properties in the lower animals, that some philosophers have regarded the human 

 intelligence as distinct in nature as well as in amount. Although we are by no means 

 prepared to accept this proposition, regarding, as we must, the intelligence of man as 

 simply superior in development to that of the lower animals, it is evident that this differ- 

 ence in the degree of development is so enormous as to render the human mind hardly 

 comparable with the intellectual attributes of animals low in the scale. But, when the 

 human brain is slightly developed, as in idiots, or when the intellectual faculties are 

 simply diminished in activity, as in certain cases of disease, the being is reduced to a con- 

 dition very like that of some of the lower animals. 



Experiments upon different classes of animals show clearly that the brain is less 

 important, as regards the ordinary manifestations of animal life, in proportion as its rela- 

 tive development is smaller. For example : if we remove the cerebral hemispheres in 

 fishes or reptiles, the movements which we call voluntary may be but little affected ; 

 while, if the same mutilation be performed in birds or some 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 

 the feeble intelligence possessed by these animals is not destroyed by the operation. It 

 is not only possible, but probable, that, in the very lowest of the vertebrates, the func- 

 tions of the nervous centres are not the same as in higher animals. There is, for exam- 

 ple, a fish (the lancet-fish, Amphioxus lanceolatus), that has no brain, all of the functions 

 of animal life being regulated by the gray substance of the spinal cord. It is essential, 

 in endeavoring to apply the results of experiments upon the brain in the lower animals 

 to human physiology, to isolate, as far as possible, the distinct manifestations of intelli- 

 gence,'from automatic movements. Bearing in mind, then, the difficulties of the ques- 

 tion and the caution with which all observations upon the great nerve-centres of the 

 lower animals must be received in their applications to pure human physiology, we shall 

 proceed to discuss the phenomena following removal or injury of the cerebrum in direct 

 experiments. 



In 1822 and 1823, Flourens communicated to the French Academy of Sciences his 

 remarkable observations upon the different parts composing the encephalon. His experi- 

 ments are so familiar to physiologists, that it is only necessary here to give his general 

 conclusions. As regards the cerebral hemispheres, he found that the 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 even of 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 opinion that animals deprived of their cerebral lobes possessed sen- 

 sation, but had lost the power of perception, and that they could execute voluntary 

 movements when an irritation was applied to any part, but had lost the power of making 

 such movements in obedience to a spontaneous effort of the will. One of the most 

 remarkable phenomena observed was entire loss of memory and of the power of connect- 

 ing ideas. ^The voluntary muscular system was enfeebled but not paralyzed. Eemoval 

 of one hemisphere produced, in the higher classes of animals experimented upon, enfee- 

 blement of the muscles upon the opposite side, but the intellectual faculties were in part 

 or entirely retained. Removal of even a considerable portion of both hemispheres was 

 followed by no very marked effect as regards the intelligence. 



The observations of Flourens have been repeated by numerous experimentalists and 



