TO RELATIVE CAPACITY OF RACES. 213 



seemed to account for his triumph over the depressing influences of 

 his limited sphere, the fact that his brain appears to have been rather 

 belovr than above the average size, points to some other requisite 

 than mere cerebral mass as essential to intellectual vigour. 



The brain is influenced in all its functions by the character and 

 the amount of blood circulating through it, and promptly manifests 

 the efl'ects of any deleterious substance, such as alcohol or opium, 

 introduced into its tissues. It depends, like other portions of the 

 nervous system, on an adequate supply of nourishment. In both 

 respects the brain of the Ayrshire poet was injuriously afiected, in 

 so far as we may infer from all the known circumstances of his life. 



The human brain is large in proportion to the body in infancy and 

 youth; and the opinions of leading anatomists and physiologists early 

 in the present century favoured the idea that it attained its full size 

 within a few years after birth. Professor Soemmering assumed this 

 to take place so early as the third year. Sir William Hamilton 

 explicitly stated his conclusion thus : "In man the encephalon 

 reaches its full size about seven years of 'age ;" and Tiedemann assigns 

 the eighth year as that in which it attains its greatest development. 

 But the more accurate and extended observations since carried on 

 rather tend to the conclusion that the brain not only goes on increas- 

 ing in size and weight to a much later period of life, but that, under 

 exceptionally favouring circumstances, it may increase in weight long 

 after the body has attained its maximum. 



The largest average brain-weights, as determined by observations 

 on the brains of upwards of two thousand men and women in different 

 countries of Europe, have indeed been found in those not above twenty 

 years of age ; and from a nearly equal number of English examples, 

 Dr. Boyd determines the period of greatest average weight to be the 

 interval between fourteen and twenty years of age ; but this includes 

 cases in which death has ensued from undue or premature brain 

 development. 



Other evidence leaves no room for doubt that cases are not rare 

 of the growth, or increased density of the brain up to middle age ; 

 while the observations of Professor Welcker indicate this process 

 extended to a later period of life. The average brain-weights, as 

 given by Boyd, Peacock, and Broca, from healthy or sane cases, 

 along with those of Welcker, include the weights of forty-seven 

 male brains from ten to twenty years of age, giving an average of 



