Donaldson, Brain and Spinal Cord of Rat. i6i 



y + 134 



143 



10 - 15 (4') 



where X represents the body weight and y the body length. 



On the basis of the body weights thus determined the weight of 

 the brain can be culeulated by the revised forniuhi (8) 



1.5G /.. u TN .569 n-jiR =^ / ^.1.56 



log X 1-^^ (x - 8.7) -^^^ - 0.316 V 



y = — " 



/ X 1-^^ \ 



2 o V ^ (x - 8.7) 



r^ '- . ' .1 (8) 



Ll + (logx) « 1 + (logx) "-'J 



as given by Hatai, '09, in this number of this journal, in which 

 y represents the weight of the brain and x the body weight. 

 The computation is simpler, however, if we use 

 y := .554 +' .569 log (x — 8.7) ... (1) (Donaldson, '08) 

 when X > 10, and a special formula 



y — 1.50 log (x) — .87... (7) (Hatai, '09) 



when X < 10, 



The results obtained from these two formulas are identical with 

 those from formula (8), and are given in the third column of 

 Table ?>. The corresponding curve is shown by the continuous line 

 on Chart III. 



When the means are determined by the aid of a correlation table, 

 in which the records are arranged in groups diifering by 10 mm. in 

 body length and 0.1 gms. in brain weight, the co-efficient of correla- 

 tion between body length and brain weight is found to be .86, which 

 is high. 



(b) The relation of the weight of the spinal cord to the body 

 length. 



When the individual records for the weight of the spinal cord 

 are plotted in relation to the body length, we obtain results which 

 are surprisingly regular. See Table 3 and Chart III (189 males, 

 137 females). 



As in the case of the determination of the brain weights, the 



