86 THE POPULAR SCIENCE MONTHLY. 



liarities in the mental faculties during disease is that the mind depends 

 greatly on the state of the body for the coordination of its various 

 powers. In health these are related in what may be called the normal 

 manner. Faculties capable of great development under other conditions 

 exist in moderate degree only, while probably, either consciously or 

 unconsciously, certain faculties are held in control by others. But 

 during illness faculties, not ordinarily used, suddenly or very rapidly 

 acquire undue predominance, and controlling faculties usually effective 

 are greatly weakened. Then for a while the mental capacity seems 

 entirely changed. Powers supposed not to exist at all (for of mental 

 faculties, as of certain other qualities, de non existentibus et de non 

 apparentibus eadem est ratio) seem suddenly created, as if by a miracle. 

 Faculties ordinarily so strong as to be considered characteristic seem 

 suddenly destroyed, since they no longer produce any perceptible 

 effect. Or, as Brown-Sequard says, summing up the results of a 

 number of illustrative cases described in a course of lectures delivered 

 in Boston, " It would seem that the mind is largely dependent on 

 physical conditions for the exercise of its faculties, and that its strength 

 and most remarkable powers, as well as its apparent weakness, are often 

 most clearly shown and recognized by some inequality of action in 

 periods of disturbed and greatly impaired health." Comhill Magazine. 



ON SENSATION AND THE UNITY OF STRUCTURE 

 OF SENSIFEROUS ORGANS. 



By Peofessoe T. H. HUXLEY. 



THE maxim that metaphysical inquiries are barren of result, and that 

 the serious occupation of the mind with them is a mere waste of 

 time and labor, finds much favor in the eyes of the many persons who 

 pride themselves on the possession of sound common sense ; and we 

 sometimes hear it enunciated by weighty authorities, as if its natural 

 consequence, the suppression of such, studies, had the force of a moral 

 obligation. 



In this case, however, as in some others, those who lay down the law 

 seem to forget that a wise legislator will consider, not merely whether 

 his proposed enactment is desirable, but whether obedience to it is pos- 

 sible. For, if the latter question is answered negatively, the former is 

 surely hardly worth debate. 



Here, in fact, lies the pith of the reply to those who would make 

 metaphysics contraband of intellect. Whether it is desirable to place 

 a prohibitory dutv upon philosophical speculations or not, it is utterly 

 impossible to prevent the importation of them into the mind. And it 



