Hee C..A. STEWART 
In these cases, however, the relative size of the brain stem 
in the brain of the stunted rats corresponds approximately to 
that in normal brains of the same weight. The only exception 
is that of the single test rat in which the brain stem should be 
relatively slightly smaller than in the control, according to the 
change found in the normal brains of corresponding weights. 
The difference is slight, however, and may be obscured in this 
case by individual variation or experimental error. 
-On the whole, therefore, it appears that during the persistent 
growth of the brain, in very young rats stunted by underfeeding, 
the brain stem (midbrain, pons, and medulla) maintains approxi- 
mately the same relative size as in the normal brain of corre- 
sponding weight. 
CEREBELLUM 
Calculations from the data obtained show that during post- 
natal growth the cerebellum (table 1) apparently increases 
rapidly from an average of about 3.7 per cent of the total weight 
of the separate parts of the brain at birth (sexes combined) to 
about 14 per cent at seven weeks of age, and maintains approxi- 
mately this relative weight in the adult albino rat. In general 
these results agree fairly well with those obtained by Hatai 
(15) (for adult rats of body length similar to that of my adult 
controls), by Sugita (’17) (from birth to 150 days of age), and by 
Donaldson (unpublished data). 
In the rats underfed for various periods the cerebellum (table 
2) shows a remarkable growth. In the individuals held at birth 
weight the cerebellum has increased from an average of 0.0077 
‘gram in the controls (sexes combined), to 0.0287 gram, an 
increase of over 272 per cent. At three and eight weeks of age 
the increase in the test rats is approximately 113 and 118 per 
cent, respectively, as compared with the younger controls of the 
same body weight. 
As to relative proportions, the cerebellum is in all cases found 
relatively much larger in the brain of the test rats, in comparison 
with that in control rats of the same body weight. If the per- 
centage of the brain weight formed by the cerebellum in the test 
