Donaldson, Grotvth of Central Nervous System. 373 



rat when the sexes are compared, it follows that similar relations 

 are found in that animal and the calculations show them. 



In view of these facts, and in view of the preceding determi- 

 nations, that for like body weights, the human male and female 

 have approximately the same weight of the brain, it necessarily 

 follows that where the body weights are alike, the spinal cord in 

 the woman is heavier than in the man; a conclusion which I be- 

 lieve has not been heretofore explicitly stated. It thus appears 

 that in both sexes of man and the albino rat, the relations of the 

 weight of the brain and the spinal cord to that of the body are 

 similar. 



From the observations presented in the later portion of this 

 paper, we conclude that man and the rat are similar in the weight 

 relations of their brain and spinal cord, in the form of the growth 

 curves for the brain, in the fraction of the span of life taken for 

 the rapid growth of the brain, and in the proportional develop- 

 ment of the brain and cord during this phase. 



They differ, however, in the intensity of the general growth 

 processes, which are some thirty times more rapid in the rat than 

 in man, in the relation of the completion of the phase of rapid 

 growth to the appearance of puberty and in the longer continuance 

 of the phase of slow growth in the rat. 



Nevertheless, in view of the similarities above named, it appears 

 that by the study of the nervous system of the albino rat, it will 

 be possible to obtain information bearing on certain growth phe- 

 nomena in man, the direct study of which in the human nervous 

 system is at present impracticable. 



