618 NERVOUS SYSTEM. 



The observations of Flourens have been repeated by many physiologists, 

 and were in the main confirmed, except as regards the special senses. Bouil- 

 laud (1826) made a large number of observations upon pigeons, fowls, rab- 

 bits and other animals, in which, after removal of the hemispheres, he noted 

 the persistence of the senses of sight and hearing. Longet finally demon- 

 strated the fact that both sight and hearing are retained after extirpation of 

 the hemispheres, even more clearly than Bouillaud, by the following experi- 

 ments : He removed the hemispheres from a pigeon, the animal surviving 

 the operation eighteen days. When this animal was placed in a dark room 

 and a light was suddenly brought near the eyes, the iris contracted and the 

 animal winked ; " but it was remarkable, that when a lighted candle was 

 moved in a circle, and at a sufficient distance, so that there should be no 

 sensation of heat, the pigeon executed an analogous movement of the head." 

 An examination after death showed that the removal of the cerebrum had 

 been complete. An animal deprived of the hemispheres also opened the eyes 

 at the report of a pistol and gave other evidence that the sense of hearing 

 was retained. 



With regard to the senses of smell and taste, it is more difficult to deter- 

 mine their presence than to ascertain that the senses of sight and hearing are 

 retained. It is probable, however, that the sense of smell is not abolished, 

 if the hemispheres be carefully removed, leaving the olfactory ganglia intact ; 

 and there is no direct evidence that extirpation of the cerebrum affects the 

 sense of taste ; indeed, in young cats and dogs, Longet has noted evidences 

 of a disagreeable impression following the introduction of a concentrated 

 solution of colocynth into the mouth, as distinctly as in the same animals 

 under normal conditions. 



Comparative Development of the Cerebrum in the Lower Animals. It is 

 only necessary to refer very briefly to the development of the cerebrum in 

 the lower animals as compared with the human subject, to show the connec- 

 tion of the hemispheres with intelligence. In man the cerebrum presents a 

 large preponderance in weight over other portions of the encephalon ; and 

 in some of the lower animals the cerebrum is even less in weight than tho 

 cerebellum. In man, also, not only the relative but the absolute weight of 

 the brain is greater than in lower animals, with but two exceptions. Todd 

 has cited a number of observations made upon the brains of elephants, in 

 which the weights ranged between nine and ten pounds (about 4,000 and 

 4,500 grammes). Rudolphi gave the weight of the encephalon. of a whale, 

 seventy-five feet long (about 23 metres), as considerably over five pounds 

 (about 2,300 grammes). With the exception of these animals, man possesses 

 the largest brain in the zoological scale. 



Another interesting point in this connection is the development of cere- 

 bral convolutions in certain animals, by which the relative quantity of gray 

 matter is increased. In fishes, reptiles and birds, the surface of the hemi- 

 spheres is smooth ; but in many mammalia, especially in those remarkable for 

 intelligence, the cerebrum presents a greater or less number of convolutions, 

 as it does in the human subject. 



