Donaldson, Growth of Central Nervous System. 357 



As in the case of the brain, however, it seems justifiable to treat 

 the sexes together. When so treated, the theoretical curve as 

 shown by the continuous line (C) in chart 3 is found by the 

 formula [3] 



y = •585(>^ + 2i) -0.795 



in which y is the weight of the spinal cord and x the body weight. 

 This formula [3] was derived in the same manner as formula [i]. 



The means for the weight of the spinal cord, determined as in 

 the case of the brain, follow this curve closely (see chart 3), The 

 numerical values for the means are given in table i, column H. 



The coefficient of correlation between body weight and spinal 

 cord weight is still higher than that for the brain, being 0.8564 

 ± 0.0071. As in the case of the brain, there is a "sag" of the 

 observed merans below the theoretical curve, between the body 

 weights of 50 and 100 gms. and what has been stated apropos 

 of this on p. 352 applies to the cord also. 



A moment's inspection of chart 3 shows that the growth of the 

 spinal cord differs from that of the brain in being on the whole 

 more rapid, and also longer continued. The details of the rela- 

 tions will be taken up later, but the point of importance 

 at this moment is that from the longer continued rapid 

 growth it follows that the increase in the weight of the cord in a 

 simple fixed relation to the body weight does not extend as far 

 down the curve as in the case of the brain. From the heaviest 

 group (315 gms.), the mean cord weight of which is taken as the 

 standard, the weight of the cord diminishes in each successive 

 group according to the 2.7th root of the body weight, until the 

 205 gms. group is reached, when the values on the logarithmic 

 curve and those determined by the 2.7th root of the body weight 

 become identical. As in the case of the brain, we consider this 

 point of intersection of the two lines to mark the cessation of rapid 

 growth. As far down as the 205 gms. group, then, the weight 

 of the spinal cord is in a simple relation to that of the body weight. 

 Using this fact as a criterion, w^e may look upon the earlier growth 

 of the spinal cord up to the 205 gms. group as rapid, while after 

 that it is slow. 



As in the case of the brain, so in the spinal cord, the varia- 

 tions in the growth of the body which produce "giants" or 

 "dwarfs," or the stunting which may be brought about experi- 



