CORRELATION OF BRAIN AND SPINAL CORD. 513 



Notwithstanding the non-elimination of the age factor, the 

 associations reported by Donaldson (6) between body weight and 

 brain weight, body weight and spinal cord weight, and the brain 

 and spinal cord in his series of rats are of the same order of 

 magnitude as those found in this study. The association between 

 cranial capacity and body weight in the female as recorded by 

 Hatai (7) is also of the same order of magnitude as my value for 

 body weight and brain weight correlation. Aside from these 

 similarities the data are rather widely divergent. 



Turning now to the analysis of my data it is evident that there 

 is a high degree of positive correlation between the several pairs 

 of variables under investigation. Neglecting the brain-spinal 

 cord weight correlation (V 3 4 ) it is seen that the order of increasing 

 degree of association is the same in both sexes. This indicates 

 that the association of the brain and spinal cord with the body 

 as a whole is governed by factors which are largely independent 

 of sex determinants of association. These independent factors 

 are probably specific in origin. 



The degree of association between brain weight and spinal cord 

 weight (/ 3 4 ) is practically the same in the female as in the male. 

 This indicates that the correlation is independent of the sex 

 differences in body size which exist in animals of the same age. 

 That is to say the association between these two parts of the 

 central nervous system is independent of sex factors contributive 

 to differences in differential development. It is, however, de- 

 pendent on other factors. While it is possible that specificity 

 plays an important part in the determination of the association, 

 I am inclined to believe that the basis of the reaction lies rather 

 in the community of characteristic chemical make-up of the two 

 organs, with the consequent similarity in response or resistance 

 to extraneous influences. Not to be neglected is the idea that 

 the chemical similarity conditions a similarity in the processes 

 of growth and hence association in weight. 



The association between body weight and body length (r\ 2 ) 

 is consistently greater than that between the other pairs of 

 variables. Nevertheless, the superiority is statistically valid in 

 but 50 per cent, of the comparisons. The general trend of 

 difference is uniform, however, and if accepted as significant is 



