Xo. .)09] 



NOTES AND LITERATUBE 



nvimber, sex, age in days, body weight, brain weight, and spinal 

 cord weight, each in grams. That the utmost care was taken to 

 ensure the accuracy of these weight records really does not need 

 saying in an American biological journal. The body weights 

 are recorded to a tenth of a gram, and the brain and cord 

 weights to a ten-thousandth of a gram. These unique data, in- 

 volving thirteen years in the collecting, constitute a scientific 

 achievement of much significance, not alone because of the in- 

 trinsic importance of the records for the study of growth prob- 

 lems, but also because they are a monumental example ot biolog- 

 ical data collected with physico-chemical exactness. The paper 

 will stand as a classic in the literature on growth. 



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

 rat's brain. The brain-weight data are plotted to a base line of 

 body weight instead of to a base line of age and when so arranged 

 are graduated with a curve of the general type. 



y = A + C log (X + p) 

 where >) denotes brain weight, x body weight and A. ( and fi are 

 constants. 



The actual theoretical curve for the brain weight of the white 

 rat is as follows: 



y = M9 log (s — 8.7) +.554. 

 This curve ffives a verv excellent graduation of the observa- 



the rat's brain in weight is of the same general type wtnen 

 has been found by Pearson and by the present writer to describe 

 growth changes in various organisms.' It is all the ti^beoom- 



for growth^Jrk. Experiences showing that it undoubtedly 

 has a wide range of applicability in describing the quantitative 

 changes occurring in growth and various sorts of r.»_ml;,t..ry 

 phenomena. While this fact is empirically obvious no ulterior 

 biological significance is to be attached to it. The biological 

 significance of this fact appears to ^ he d . preSen * ^ha^ some par 



