210 MENTAL AND PHYSICAL EXERCISE 



which they exhibited. The examination has also been 

 extended to the inferior animals and the same principles 

 have been applied to their sculls, both as to what respects 

 their general form, and the proportionate size of their 

 individual parts, whether indicating a generic, or an indi- 

 vidual difference. 



655. " In estimating the value of these arguments, 1 

 shall arrange them in two divisions, as they relate to 

 general considerations of probability, or as they depend 

 more upon particular facts. 



656. " And with respect to the first point, I think it will 

 be admitted that there is none of them that possesses more 

 than an indirect application to the question in discussion. 

 Admitting that the perfect organization of the brain is a 

 necessary intermedium for the exercise of the mental 

 powers, we may conclude, that every part of this organ 

 must have a necessary connection with the exercise of 

 these powers, as every part of the eye and the ear has a 

 reference to the production of vision and of sound. In 

 consequence of our knowledge of the physical laws of 

 light, and the undulation of the air, we are enabled to 

 trace out the mode in which the several parts of the eye, 

 and of the ear, co-operate to produce the ultimate effect. 

 Had we the same knowledge of the mode in which the 

 mind operates upon the brain, we should probably have 

 it in our power to detect the same kind of co-operation 

 of all its parts and structures to the production of percep- 

 tion and thought. But on this point we are in total igno- 

 rance, and therefore, although w T e may go so far as to 

 assert, that a perfect brain, in a certain sense, is essential 

 to a. perfect mind, we are unable to say in what way 

 it is so. 



657. " The only anatomical argument which is of so 

 tangible a nature as to allow of anything approaching to 

 direct deduction, is derived from a consideration of the 

 degree in which an injury of the brain produces a cor- 

 responding injury of the mental powers. Upon this 

 point I have already stated my opinion, and I have only 

 to add, that while the connection is not of that nature 

 which indicates the relation of cause and effect, so I 

 should be still less disposed to allow, that the facts 

 which we possess are of that distinct and direct nature, 



