$34 THE NERVOUS SYSTEM. 



exercises ; so that it is not certain that one hemisphere 

 will suffice for these. In general, the mind 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 destruc- 

 tion or compression of either hemisphere, whatever effects 

 are produced in loss of sensation or voluntary motion, are 

 observed on the side of the body opposite to that on which 

 the brain is injured. 



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 appro- 

 priate for the exercise 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: I. That it is in 

 accordance with the physiology of the other compound 

 organs or systems in the body, 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 

 mental functions are manifested in very different degrees. 

 Even in early childhood, before education can be imagined 

 to have exercised any influence on the mind, children 

 exhibit various dispositions each presents some predomi- 

 nant 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 



