WEIGHT OF BRAIN 221 



Twenty to thirty years 45 grams. 



Thirty-one to forty-one years . . 50 grams. 



Sixty years 60 grams. 



The ventricles have a capacity of 26 c.c. of water. 



In considering the weights of different brains, it is assumed 

 that the proportion of nervous to non-nervous tissue is constant, 

 so that different weighings may be compared. If this be the 

 case, then the variations in weight may be due to greater size 

 of the individual nerve elements, indicating a greater potential 

 energy, or they may be due to a greater number of nerve ele- 

 ments giving rise to more possible pathways. A minute study 

 of the proportional weights of different parts of the brain shows 

 that variations due to sex, age, and stature are very constant, 

 which is in harmony with the view that weight differences are 

 due to the size of the nerve elements rather than to variations 

 in their number. In the latter case brain weights would show 

 independent variations in different parts of the encephalon. 



All parts of the central nervous system of males are heavier 

 than corresponding parts of females. The weight varies, in 

 each, directly with the stature and inversely with old age. 

 The brains of criminals do not differ in any marked way from 

 those of ordinary hospital patients. Insane (excluding micro- 

 cephalies) have no characteristic brain weight, except in such 

 cases where a congestion of the brain has occurred, when the 

 weight is markedly increased; on the other hand, insanity due 

 to destructive changes of brain tissue is marked by a low 

 brain weight. As a whole, individuals whose brains during 

 the years of growth have been under favorable circumstances 

 possess the heavier brains. In some degree the size of the brain 

 bears a direct relation to the intellect of the individual, but this 

 is not absolute. The depth of the sulci and the consequent size 

 and complexity of the convolutions are a more efficient measure 

 of the brain power. In the largest of the apes the brain of 

 an adult animal is about the same in weight as that of a 

 human infant at birth. 



Weight of Cord. The average weight of the spinal cord is 

 about 26.67 grams, without the nerve roots, but the pia intact. 

 It is probable that this weight varies, like that of the brain, 

 with age, sex, and stature. 



