364 'Journal of Comparative Neurology and Psychology. 



0.369 gm. to 2.820 gms., or 7.9 times, and as calculated, from 

 0.264 gm. to 2.652 gms., or 10 times. 



2. That for the central nervous system, the period of rapid 

 growth extends up to the 135 gms. group, after which the system 

 increases nearly regularly in proportion to the 5th root of the 

 body weight. 



3. When the mean weights of the central nervous system are 

 determined according to sex, it appears that in 68 per cent of the 

 records the weight in the male exceeds that in the female, but on 

 the average the difference is small, amounting to only 0.8 per 

 cent. 



4. From birth to the 15 to 25 gm. group, the brain grows more 

 rapidly than the spinal cord, but after that the spinal cord grows 

 faster, so that using the calculated values, the ratio drops from 

 8.74 at 15 gms. to 2.85 at 315 gms. 



5. The coefficient of correlation between the weight of the 

 brain and the weight of the spinal cord is very high, being 0.8787 



± 0.006. 



COMPARISON OF THE GROWTH OF THE BRAIN AND OF THE 



SPINAL CORD IN THE ALBINO RAT, WITH THEIR 



GROWTH IN MAN. 



With the foregoing data in hand, it is possible to make some 

 comparisons between man and the albino rat in respect to the 

 growth of the brain and of the spinal cord. 



Five points will be examined: 



1. The form of the growth curve according to age. 



2. The relative increase in the weight of the brain during the 

 phase of rapid growth. 



3. The time taken for this increase. 



4. The cessation of the rapid growth of the brain in relation to 

 puberty. 



5. Weight of the brain and the spinal cord as modified by sex. 

 To determine in the albino rat the growth of the brain with age, 

 the calculation according to the formula [i] was made for the 

 brain weight of each of the age groups used by me in constructing 

 the growth curve for the entire body (Donaldson '06). The 

 results obtained are given in the following table 9 and are plotted 

 in chart 5, plate iii. 



