362 'Journal of Comparative Neurology and Psychology. 



diminishes. The observed values indicate the same relation, 

 although in a less marked degree. The accompanying table 7 

 shows this ratio, determined for each of the several body weight 

 groups. 



The phase in which the brain grows relatively more rapidly than 

 the spinal cord is found also in man, but so far as the scant 

 human records go it appears to pass over into the phase of the less 

 rapid relative growth of the brain some time before birth (Mies 

 '93). Owing to the immaturity of the rat at birth, however, this 

 earlier phase is just recognizable as a post-natal phenomenon in 

 that animal. 



The mean values for the weight of the spinal cord at given brain 

 weights are represented by the dots in chart 4, and are given 

 under ''observed" in table 8. In this same table under "calcu- 

 lated" are given also the values for the weights of the spinal cord 

 as determined by calculation. These latter values were obtained 

 in the following manner. Transposing formula [i] to the form 



Log. {x - 8.7) = I -:ii^ or X = 8.7 + 10 -5^9 



•569 



it was possible to calculate the body weights which belonged to 

 the brain weight values used in this table. From the body weights 

 thus obtained the corresponding weights for the spinal cord were 

 calculated by formula [3]. The continuous line in chart 4, p. 363, 

 is the curve based on these values, and the inspection of the chart 

 shows that the observed values and those calculated agree very 

 closely. 



On correlating the brain weight with the observed spinal cord 

 weight, using weight groups for the brain differing by o.i gms., 

 the coefficient of correlation is found to be 0,8787 ± 0.006, which 

 is higher than for any relation which we have had occasion to deter- 

 mine. Pfister ('03), in his studies on the spinal cord and brain 

 in children, has also noted the close correlation between these two 

 portions of the central nervous system. 



From the foregoing study of the weight of the entire central 

 nervous system and of the relation of the brain weight to that of 

 the spinal cord, we conclude : 



I. That from the 5 to the 315 gms. weight group, the entire 

 central nervous system as observed, increases in weight from 



