110 THE GROWTH OF THE BRAIN. 



it appears that between birth and maturity the weight 

 of the cord has increased over 7^ fold, as against an 

 increase in the weight of the brain of less than one-half 

 that amount. The proportional relations of the ence- 

 phalon to the cord at different ages are very interesting. 

 In the case of a three months' foetus the brain weighed 

 1 8 times as much as the cord ; in the foetus of five 

 months it was 101 times heavier ; and in the case of 

 21 children born at full time (n females and 10 males) 

 it was almost 115 times heavier. On the other hand, in 

 10 men at maturity the brain weighed 513 times the 

 weight of the cord, and in 4 females the proportional 

 weight was 49*47. There are, however, no published 

 figures concerning the growth of the cord during the 

 first twenty-five years, so that this process cannot be 

 compared in detail with the growth changes taking 

 place in the brain. But from the foregoing it is to be 

 seen that in proportion to that of the brain the increase 

 in the weight of the cord in early foetal life is rapid, at 

 the time of birth slow, and then more rapid up to 

 maturity. 



With the increase of the central nervous system, 

 occur changes in its composition concerning which a few 

 observations exist. In its first form the entire central 

 system is grey, and only later do portions of it become 

 white by the development of myeline in the sheaths of 

 the nerve fibres. The myeline contains fatty substances 

 and a smaller proportion of water than the axial part of 

 the fibre which it ensheaths. The following table indi- 

 cates the proportion of water and myeline (extracted by 

 ether) found in the white matter (fibres of the callosum) 

 at birth and at maturity. 1 



1 Schlossberger, Ann. der Chemie u. Pharmac., 1853. 



