350 'Journal of Comparative Neurology and Psychology. 



body, a condition which would also modify the results w^hich we 

 have obtained by using the crude body weights alone. 



In view of these circumstances, it seems permissible in most 

 instances to treat the records for both sexes together, and so the 

 statements which follow^ are based on the total series of records 

 without distinction of sex, except where such distinction is specially 

 noted. 



The theoretical curve, about which the observations cluster, 

 is represented by the continuous line in charts i and 3, plates 

 ii and iii, and was found by means of the logarithmic formula 



[I] 



y = -569 log- (^ - 8.7) + -554 



in which y is the weight of the brain in gms. and x the weight of 

 the body in grms. This formula has already been published by 

 Hatai ('08). The values obtained are given in column D of 

 table I. 



The formula [i] just given, was derived in the following manner. 

 Assuming that the weight of the central nervous system is a func- 

 tion of the body weight, we obtain at once the following general 

 expression 



y = ^{x) 



An inspection of the curve of the brain weights, as plotted on 

 the body weights, shows that the rate of growth of the nervous 

 system decreases as the body weight increases. This relation is. 

 expressed by the following formula 



where C is a constant. 

 Hence we have 



ax X 



dy = — C, dx 



■^ X 



and 



y =C^~ dx = C log X + A 



The two constants C and A were determined by the method of 

 the least squares. 



