142 HUMAN PHYSIOLOGY. 



However important a centre the cerebrum may be, for the exhibition of 

 this highest form of nervous action, it is not directly essential for the con- 

 tinuance of life; for it does not exert any control over those automatic 

 reflex acts, such as respiration, circulation, etc., which regulate the functions 

 of organic life. 



From the study of comparative anatomy, pathology, vivisection, etc., 

 evidence has been obtained which throws some light upon the physiology 

 of the cerebral hemispheres. 



1. Comparative Anatomy shows that there is a general connection be- 

 tween the size of the brain, its texture, the depth and number of convolu- 

 tions, and the exhibition of mental power. Throughout the entire animal 

 series, the increase in intelligence goes hand in hand with an increase in 

 the development of the brain. In man there is an enormous increase in 

 size over that of the highest animals, the anthropoids. The most cultivated 

 races of men have the greatest cranial capacity; that of the educated 

 European being about 116 cubic inches, that of the Australian being about 

 60 cubic inches, a difference of 56 cubic inches. Men distinguished for 

 great mental power usually have large and well-developed brains ; that of 

 Cuvier weighed 64 ozs. ; that of Abercrombie 63 ozs. ; the average being 

 about 48 to 50 ozs. ; not only the size, but above all, the texture of the 

 brain, must be taken into consideration. 



2. Pathology. Any severe injury or disease disorganizing the hemi- 

 spheres is at once attended by a disturbance, or entire suspension of mental 

 activity. A blow on the head producing concussion, or undue pressure 

 from cerebral hemorrhage destroys consciousness; physical and chemical 

 alterations in the gray matter have been shown to coexist with insanity 

 loss of memory, speech, etc. Congenital defects of organization from im- 

 perfect development are usually accompanied by a corresponding deficiency 

 of intellectual power and the higher instincts. Under these circumstances 

 no great advance in mental development can be possible, and the intelli- 

 gence remains at a low grade. In congenital idiocy not only is the brain 

 of small size, but it is wanting in proper chemical composition; phosphorus, 

 a characteristic ingredient of the nervous tissue, being largely diminished 

 in amount. 



3. Experimentation upon the lower animals by removing the cerebral 

 hemispheres is attended by results similar to those observed in disease and 

 injury. Removal of the cerebrum in pigeons produces complete abolition 

 of intelligence, and destroys the capability of performing spontaneous move- 

 ments. The pigeon remains in a condition of profound stupor, which is 

 not accompanied, however, by a loss of sensation, or of the power of pro- 



