3/0 'Journal of Comparative Neurology and Psychology. 



chronic disease, on the other (Greenwood '05, Gladstone '05 

 and Blakeman '05). 



Turning next to the relations of puberty to the completion of the 

 rapid growth of the brain, it is worthy of note that the comple- 

 tion of rapid growth in the albino rat at about 72 days, coincides 

 in this animal with puberty, which appears at 65 to 75 days. 

 In man, on the other hand, it precedes puberty from 6 to 9 years. 

 Any interpretation of this difference must await a determination 

 of the finer anatomy of the brain in the two forms, at the time of 

 puberty. 



Passing to the spinal cord, much less can be done in the way 

 of comparison owing to the small amount of data on the spinal 

 cord of man. The human spinal cord at birth has a mean w^eight 

 of about 3.2 gms. (Mies '93) and at maturity of 27 to 28 gms. 

 (Ziehen '99). The body weight, length of trunk and sex prob- 

 ably all have an influence on the weight of the cord, but we do 

 not know how much (Pfister '03). 



Using the foregoing values (3.2 gms. and 27.5 gms.) it appears 

 that between birth and maturity the human spinal cord increases 

 in weight about 8.6 times. Taking the calculated weight of the 

 spinal cord in the rat (mean of both sexes) as 0.589 gm. at 303 

 days (equal to 25 years of human life), we find that the weight 

 which would give an increase of 8.6 times is 0.068 gm. This 

 corresponds to the average weight of the cord between 7 and 8 

 days, which is nearly the same as the age (5 to 6 days) found for 

 the brain by a like calculation. From this it follows that the cell 

 elements in the spinal cord of the rat enlarge in the same propor- 

 tion as do those in man, and that these two divisions of the central 

 nervous system in the rat are similarly related to the correspond- 

 ing parts in man. Calculation shows that the amount of enlarge- 

 ment between birth and maturity is in both forms very nearly 

 2.5 times greater in the case of the spinal cord than it is in the case 

 of the brain. Expressing this result in terms of neurones, it 

 would mean that the average bulk attained by the neurones of the 

 spinal cord was 2.5 greater than that attained by the nuerones of 

 the brain. The relatively greater weight of the cord of the rat, 

 as compared with the brain, depends of course, on the initial plan 

 of the central nervous system peculiar to that animal. 



With regard to the weight of the brain and of the spinal cord as 

 modified by sex, a few words are in place. In the human records, 



