30 AN INTRODUCTION TO SCIENCE 



then it has been shown (i) that stimulation of particular 

 areas of the cortex results in definite movements, while 

 removal of the said areas is followed by paralysis for these 

 movements, and (2) that almost the whole of the cortex can 

 be mapped into territories which are occupied by the several 

 senses. It is true that a region is left in the front of the 

 brain corresponding with the forehead, which cannot at 

 present be associated w T ith either movement or sensation ; 

 but, although its functions are unknown, there are ample 

 grounds for believing that the mind makes no greater use of 

 this region than of the regions behind it. For instance, this 

 anterior region may be found to be healthy in cases in which 

 the mind was most hopelessly deficient or deranged ; or, on 

 the other hand, this region may be extensively injured, and 

 yet no mental deficiency be recorded. This does not show 

 that it is not concerned with mind, since the same may be 

 said of every other region of the cortex, but it proves that it 

 is not the special or chief seat of mind. 



If the brains of animals which are conspicuous for the 

 great acuteness of one particular sense, or for its abeyance, 

 be examined, it is easy to see which parts of the brain are 

 associated with this sense ; and it is possible to select such a 

 series of animals as will show an excessive or deficient 

 development of each of the five senses. A dog shows a 

 vast development of the sense of smell ; a marine mammal 

 is totally destitute of this sense, for it is obvious that smell is 

 a sense which cannot be employed under water. The eye 

 is as useless underground as the nose under water, and it 

 may consequently atrophy completely, as in the mole. An 

 otter, twisting in and out among the snags and roots which 

 border a dark brown peat-stained mountain stream, searches 

 for the fish which "sulk," to use a piscatorial term, under 

 the overhanging banks. Its eye is almost as useless to the 

 otter as its nose, and it consequently relies for information 

 chiefly upon the extraordinarily sensitive bristles of its cheek 

 and lip. Again, anyone who watches a cat will see that its 



