Donaldson, Grozvth of Central Nen^ous System. 355 



usual conditions, nor by the deficient growth which may be experi- 

 mentally induced. 



From the foregoing observations on the albino rat we conclude: 



1. That for albino rats between 5 and 315 gms. in body weight 

 the mean weight of the brain as observed increases from .333 gm. 

 to 2.083 gms., or 6.2 times, and as calculated, from .231 gm. 

 to 1.969 gm. or 8.5 times. 



2. That from birth up to a body weight of about 105 gms. 

 the brain grows rapidly, and after that, more slowly, increasing 

 in the phase of slow growth very nearly as the 7th root of the body 

 weight. 



3. That the weight of the brain is closely correlated with the 

 body weight, the coefficient of correlation being 0.7639 ± 0.0108, 

 but less closely correlated with the age, the coefficient of correla- 

 tion being 0.5177 ± 0.0261. 



4. That the relation of the brain weight to the body weight 

 is not essentially modified in either "dwarf" or "giant" individ- 

 uals, nor in those experimentally stunted. 



5. That in these various relations there is no marked distinc- 

 tion between the sexes, although on the average for animals of 

 the same crude body weight, the male has a brain weight 1.5 per 

 cent heavier than that of the female. 



The bearing of these results on the corresponding relations as 

 recorded for man will be considered farther on. 



We pass next to the observations on the growth of the spinal 

 cord. 



GROWTH OF THE SPINAL CORD. 



The general table contains 647 records (429 male, 218 female) 

 of the weight of the spinal cord. Chart 2 shows how the individual 

 observations are distributed when these are entered in relation to 

 the body weight in the same manner as in the case of the brain. 

 It has been possible to record clearly on the chart only a fraction of 

 the total records, and so 65 males and 21 females have been 

 omitted. 



The determinations of the values according to sex are given in 

 table 4, and show a distinct tendency for the female to have a 

 heavier spinal cord, as the cord is greater in weight in 68 per cent 

 of the groups, and on the average exceeds that of the male by 



