THE CEREBRO-SPINAL NERVOUS SYSTEM. 513 



tal defect was observed, although one cerebral hemisphere was so disor- 

 ganized or atrophied that it could not be supposed capable of discharging 

 its functions. The remaining hemisphere was, in these cases, adequate 

 to the functions generally discharged by both; but the mind does not 

 seem in any of these cases to have been tested in very high intellectual 

 exercises; so that it is not certain that one hemisphere will suffice for 

 these. In general, the brain combines, as one sensation, the impressions 

 which it derives from one object through both hemispheres, and the 

 ideas to which the two such impressions give rise are single. In relation 

 to common sensation and the effort of the will, the impressions to and from 

 the hemispheres of the brain are carried across the middle line; so that in 

 destruction or compression of either hemisphere, whatever effects are pro- 

 duced in loss of sensation or voluntary motion, are observed on the side 

 of the body opposite to that on which the brain is injured. 



Localization of Functions. In speaking of the cerebral hemispheres 

 as the so-called organs of the mind, they have been regarded as if they 

 were single organs, of which all parts are equally appropriate for the ex- 

 ercise of each of the mental faculties. But it is possible that each 

 faculty has a special portion of the brain appropriated to it as its proper 

 organ. For this theory the principal evidences are as follows: 1. That 

 it is in accordance with the physiology of the compound organs or sys- 

 tems in the bod} 7 , in which each part has its special function; as, for 

 example, of the digestive system, in which the stomach, liver, and other 

 organs perform each their separate share in the general process of the 

 digestion of the food. 2. That in different individuals the several men- 

 tal functions are manifested in very different degrees. Even in early 

 childhood, before education can be imagined to have exercised any in- 

 fluence on the mind, children exhibit various dispositions each presents 

 some predominant propensity, or evinces a singular aptness in some 

 study or pursuit; and it is a matter of daily observation that every one 

 has his peculiar talent or propensity. But it is difficult to imagine how 

 this could be the case, if the manifestation of each faculty depended on 

 the whole of the brain; different conditions of the whole mass might 

 affect the mind generally, depressing or exalting all its functions in an 

 equal degree, but could not permit one faculty to be strongly and another 

 weakly manifested. 3. The plurality of organs in the brain is supported 

 by the phenomena of some forms of mental derangement. It is not 

 usual for all the mental faculties in an insane person to be equally dis- 

 ordered; it often happens that the strength of some is increased, while that 

 of others is diminished; and in many cases one function only of the 

 brain is deranged, while all the rest are performed in a natural manner. 

 4. The same opinion is supported by the fact that the several mental 

 faculties are developed to their greatest strength at different periods of 

 life, some being exercised with great energy in childhood, others only in 

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