CH. XVI.] TEE EVOLUTION OF MIND. 135 



The convolutions into which the human brain is divided 

 by these furrows, consist for the most part of "eight distinct 

 and concentric layers, formed chiefly of closely-packed fibres, 

 and of crowds of cells of very different shapes, the layers 

 differing in the relative proportion of cells and fibres, and in 

 the manner of their arrangement." ^ Each cell sends forth 

 processes with which the tissue of certain fibres becomes 

 continuous. The office of the fibres is to establish communi- 

 cation between the cells. Between millions of these cells 

 there run millions of fibres, establishing communications in 

 all directions. And the elaborate researches of Schroede^ 

 van der Kolk have gone far to prove that the shapes of th« 

 cells and the intricacy of their communications vary with 

 the amount of intelligence. In various forms of mental 

 disease, both cells and fibres undergo pathological changes, 

 such as atrophy, hardening, softening, or some other form of 

 degeneration. That is to say, not only are the activities oi 

 the cells impeded, but the channels of communication are 

 variously obliterated or blocked up. 



quantity of brain. But the character of this relationship is seriously mis- 

 interpreted both by phrenologists and by the rest of the unlearned public. 

 It is impossible to say that a man with an unusually large head must be a 

 man of unusual mental capacit}', because the quantity of mental capacity 

 depends on many other factors besides quantity of brain. It not only 

 depends upon the sinuous creasing of the brain-surface here described, which 

 can in nowise be detected by an examination of the outside of the head, but 

 it also depends largely, as Mr. Lewes well reminds us, upon the very im- 

 portant element of vascular irrigation. " Many individual variations in 

 mental character depend on the variations in the calibre of the cerebral 

 and carotid trunks — and many variations in the intellectual, emotive, and 

 active tendencies depend on the relative importance of the cerebral and 

 carotid trinks. The energy of the brain depends mainly on the calibre of its 

 arteries ; the special directions of that energy depend on the territorial dis- 

 trihution." — Frollcms of Life and Mind, vol. i. p. 151. Again, the quantity 

 of available mental energy which can be evolved in a given period of time, 

 depends, to a very great extent, upon the efficiency with which the blood is 

 supplied with ox3'gen and freed from carbonic acid ; so that mental capacity 

 not only depends upon capacity of brain, but also apon capacity oF lungs and 

 liver. In short, a thorough examination shows that while Mind is most 

 Jirectly correlated with P.iain, it is indirectly but closely correlated with the 

 entire organism. So that the attempt to estimate individual differences in 

 mental capacity by referring to brain-size alone, is an utter absurdity. 

 * Maudsley, Physiology and Pathology of Mind, p. 55. 



