69 6 NERVOUS SYSTEM. 



pose that they may have separate and peculiar properties and functions. One of the 

 most valuable methods of investigation of the functions of these separate ganglia is that 

 of extirpation of one or more, leaving the others, as far as possible, intact. This method 

 was first employed with marked success by Flourens and has since been adopted by 

 many experimenters. It must be remembered, however, that there is no subject of 

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

 animals to the human subject, 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. 



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

 portant, 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 dimin- 

 ished power of voluntary motion is much more marked. It would be plainly unphilo- 

 sophical to assume, because a fish or a frog will swim in water and execute movements 

 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 functions of the 

 nervous centres are not the same as in higher animals. There is, for example, a fish (the 

 lancet-fish, AmpJiioxus 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 physi- 

 ology, to isolate, as far as possible, the distinct manifestations of intelligence, from auto- 

 matic movements. Bearing in mind, then, the difficulties of the question and the caution 

 with which observations upon the great nerve-centres of the lower animals must be 

 received in their applications to human physiology, we shall proceed to discuss the phe- 

 nomena following removal 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 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 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. Removal 

 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. 



The observations of Flourens have been repeated by many experimentalists and 



