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THE AMEHK AX A I / / /.'.!/./> /' [Vol.XLHI 



structures, not before known to have anything in common. 

 Such a result might mean thai these structures all had a common 

 cause or mode of origin, but to draw such a conclusion in the 

 absence of confirmatory evidence of another kind than that 

 afforded by the stain would be an exceedingly hazardous pro- 

 ceeding. 



Donaldson points out that while the logarithmic curve 

 describes very well the growth of the brain for the whole period 

 from birth to maturity, the simpler relation proposed by Dubois, 

 according to which the brain weight increases as some simple 

 proportion (here the seventh root) of the body weight, fails to 

 do this, since it holds only for the later growth period of the 

 rat's brain. It fails entirely to graduate the data during the 

 period of rapid growth. 



The second portion of the paper deals with the growth of the 

 spinal cord. This again is found to follow a logarithmic curve 

 of the same general type as that which graduates the brain 

 growth data though, of course, with different values of the 

 several constants. Succeeding portions of the paper deal with 

 the growth of the entire central nervous system and with the 

 comparison of the growth of the brain in the rat and in man. 

 Limitations of spare forbid a detailed discussion here of the 

 numerous significant results set forth in the paper. Certain 

 points of particular interest from the biometric standpoint may, 

 however, be touched upon briefly. First with regard to the 

 correlation data, Donaldson finds that the weight of the brain 

 in the white rat is very closely correlated with body weight, the 

 coefficient of correlation between these two variables being 

 .76 ± .01. This appears to indicate a very much closer relation- 

 ship in this organism than in man. though of course it must 

 always be remembered that the body weight data for man which 

 have been available for the study of this correlation are autopsy 

 records and therefore not too trustworthy. The correlation 

 found between brain weight and age is also verv much higher 

 than the corresponding correlation in the rase of man. the coeffi- 

 cient here being .52 ± .03. The spinal cord weight is found to 

 be even more closely correlated with body weight than is brain 



data available for comparison. The data presented also indi- 

 cate a very high degree of correlation between the weight of 

 the brain and the weight of the spinal cord. The coefficient of 



