GROWTH OF THE CEREBRAL CORTEX 223 
only to compare the results among themselves and not to de- 
termined the exact quantity of the extractive substances. 
Table 16 gives for each group in this study the ratio of the 
brain weight after dehydration in 80 per cent alcohol (for twenty- 
four hours) and in 90 per cent alcohol (for twenty-four hours) to. 
its initial weight in the fresh condition, calculated in the same 
way as in table 15 and each paired with the standard ratio for 
the same age, quoted from table 15. Thus compared, the under- 
fed brains show in general a higher ratio, the difference amounts 
to 1.0-4.3 per cent, on the average 1.9 per cent, while the differ- 
ence in the control brains is generally low, on the average 
+ 0.4 per cent. 
This examination tells us roughly that in the underfed brains 
the alcohol-extractives are somewhat less in quantity than in 
‘the normal brain, if the age be taken as the standard of compari- 
son, and, therefore, it may be concluded that they are somewhat 
retarded in the formation of alcohol-extractive substances and 
therefore in myelination. Reviewing tables 14 and 16 together, 
we see that during underfeeding the myelination process or the 
increase in the alcohol-extractives is retarded slightly, but is 
going on, not greatly affected by the outside influence, regularly 
according to its age. It is fair to say, however, that the differ- 
ences thus determined by extraction are seemingly less than those 
shown by the histological tests. 
15. A DISCUSSION ON THE RELATION BETWEEN THE BODY 
WEIGHT AND THE BRAIN WEIGHT IN THE UNDERFED 
ALBINO RATS 
By examining table 4 it will be readily seen that under severe 
underfeeding at an early age, the increase in the body weight and 
the brain weight, according to the age, is notably reduced, and, as 
a consequence, the acutely underfed (Series I, chapter 5 and 
table 1) have lost, in the course of first twenty days after birth 
(during suckling period), about 29 per cent in body weight, but 
only 8 per cent in brain weight, when compared with the corre- 
sponding standard values for the same age. By chronic starva- 
tion, during which the young (excessive in number) were left 
