THE CEREBRAL HEMISPHERES. 695 



It comprehends, it is true, the facts deduced from experiments upon living animals, but 

 the results obtained by this method are comparatively few and their scope is restricted. 

 Nevertheless, they are sufficiently definite ; and, if these results be corrected and applied 

 to the human subject by a comparison with pathological facts, there still remains in psy- 

 chology much that may be regarded as within the range of experimental physiology ; for 

 pathological cases are very frequently available to the physiologist as accidental experi- 

 ments indicating the functions of parts of the human organism. We cannot restrict 

 ourselves, however, to this method in the study of the intellectual phenomena ; and we 

 must draw upon facts in comparative anatomy and physiology, anthropology, and, finally, 

 upon the direct observation and classification of the intellectual processes. 



The experimental physiologist has shown that the encephalon may receive impres- 

 sions and appreciate them as sensations ; that impressions may be here connected and 

 give rise to various of the phenomena of animal and intellectual existence; that im- 

 pressions are recorded by the memory; and, finally, that certain parts are endowed 

 with special functions. But beyond this, psychology is a science mainly of introspec- 

 tive observation, the facts contributed by the experimentalist being few and barren. 

 The observer of intellectual phenomena studies the process of development of the 

 mind ; he soon separates the instinctive phenomena, observed in the lower animals 

 and in the human being without experience, from the acts which follow experience, 

 observation, the recording of impressions by memory, and the generation of ideas ; he 

 brings his perfected intelligence to bear upon the process of development of the same 

 kind of intelligence in the human being progressing from infancy to adult life; and, 

 finally, the psychological philosopher attempts, by introspective observation, to study 

 the workings of the perfect intellect, his only means of investigation being the very 

 intelligence he is endeavoring to comprehend. 



At the present day, we are in possession of a sufficient number of positive facts to 

 render it certain that there is and can be no intelligence without brain-substance; that, 

 when brain-substance exists in a normal condition, intellectual phenomena are manifested, 

 with a vigor proportionate to the amount of matter existing; that destruction of brain- 

 substance produces loss of intellectual power ; and, finally, that exercise of the intellectual 

 faculties involves a physiological destruction of nervous substance, necessitating regenera- 

 tion by nutrition, here, as in other tissues in the living organism. The brain is not, strictly 

 speaking, the organ of the mind, for this statement would imply that the mind exists as 

 a force, independently of the brain ; but the mind is produced by the brain-substance ; 

 and intellectual force, if we may term the intellect a force, can be produced only by the 

 transmutation of a certain quantity of matter. 



In treating of the functions of the cerebrum, we shall not discuss psychology, except 

 in so far as physiologists have been able to connect the mind, taken as a whole, with a 

 distinct division of the nervous system. In this we shall draw upon experiments on living 

 animals, facts in comparative physiology, in pathology, and, to a certain extent, the rela- 

 tions clearly shown to exist between the development of intelligence and certain of the 

 nerve-centres, in different races of men and different individuals. With regard to the 

 location of particular functions in distinct portions of the cerebrum, we have but little 

 definite knowledge, beyond the experiments already cited in treating of the irritability 

 of the cerebral substance, and the probable location of the faculty of speech. 



Extirpation of the Cerebrum in the lower Animals. It is, perhaps, sufficiently evident, 

 from anthropological and pathological observations as well as the study of comparative 

 physiology, that the intellectual faculties reside in the encephalon ; but these methods of 

 investigation do not clearly indicate the special functions of different parts of the cranial 

 contents. We have seen, in our general sketch of the anatomy of the brain, that this is 

 by no means a simple organ, and that certain parts, although they are hound together by 

 commissural fibres, have sufficient anatomical distinctness to lead the physiologist to sup- 



