t 
PARTS OF BRAIN IN NORMAL AND UNDERFED RATS 521 
In general, therefore, the data indicate that during the per- 
sistent growth of the brain, in very young rats stunted by 
underfeeding, the cerebrum (telencephalon and diencephalon) 
maintains the same relative size as in the normal brain of 
corresponding weight. 
BRAIN STEM 
The percentage weights (calculated from the combined weights 
of separate brain subdivisions) for the brain stem (including. 
midbrain, pons, and medulla oblongata) show a relative decrease 
from an average of about 29 per cent of the normal brain at 
birth to about 16 per cent at three weeks. Subsequently the 
growth of the brain stem is more rapid than that of the brain 
as a whole, resulting in a gradual increase in relative weight to 
an average of about 22 per cent in the adult rats. The normal 
initial decrease and subsequent increase in the relative size of 
the brain stem is in agreement with the observations by Sugita 
(17) and Donaldson (unpublished data). As compared with 
adult animals of corresponding body length, my results corre- 
spond fairly well with those obtained by Hatai (’15). 
In the stunted rats held at birth weight for various periods, 
and also in the other groups of test animals, the weight of the 
brain stem (table 2) in all cases considerably exceeds that in the 
younger controls of the same body weight. In the first group 
there is an increase from an average of 0.0618 gram (sexes com- 
bined) for the controls to 0.1064 gram in the test rats, an increase 
of approximately 72 per cent. In the test rats at three and eight 
weeks of age, the increase in brain stem weight amounts to about 
20 and 39 per cent, respectively. : 
As to relative proportions, the brain stem in the rats held at 
birth weight apparently decreases from about 29 per cent (in the 
controls) to about 22 per cent of the brain weight. In the test 
rats at 22 days the brain stem weight has further decreased to 
about 18 per cent, as compared with 19 per cent in the controls 
of similar body weight. In the test rat at 56 days, however, 
the brain stem has slightly increased to 19 per cent (18 per cent 
in the control). 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 29, NO. 5 
