OLFACTORY BULBS OF THE ALBINO RAT 203 
while the olfactory bulbs of these animals were much heavier 
than those of the albinos, the ratio between bulb weight and 
brain weight in this series was about the same in the two forms. 
Inequality in the size of the two bulbs in the same individual 
appears not infrequently in the albino and when it occurs it 
will often be found in several, and occasionally in all, members 
of the same litter. For this reason, in selecting material for 
these experiments, we discarded all litters in which cases of 
asymmetry were observed among the initial controls. 
Observations made from time to time by Dr. Donaldson, 
indicated that rats born in the early summer differ from winter- 
born rats in the relative size of the olfactory bulbs; also that 
there might be a difference between rats reared on a restricted 
diet, such as is frequently used in colonies, and those fed on the 
table-scrap diet adopted for the Wistar colony. Moreover, 
cases had appeared in which the bulbs of sick rats were appar- 
ently smaller than those of healthy individuals. 
All these facts suggested that there might be factors in, the 
living conditions of the rats which would account for the varia- 
bility of this portion of the nervous system, the growth of the 
bulbs being retarded or arrested in rats reared under unfavor- 
able conditions, such as the intense heat of the summer, or a 
monotonous diet, or in those suffering from the various infections 
which may attack the rats from time to time. 
It was, therefore, with the hope of throwing some light upon 
the question of the effect of environmental conditions upon the 
olfactory bulb of the growing albino rat, that, at the suggestion 
of Dr. Donaldson, the present experiments were undertaken. 
The problem resolved itself into two questions—Can the growth 
of the olfactory bulbs of the stock albino be modified (1) by 
underfeeding or (2) by exercise? 
The writer wishes here to express her deep gratitude to Dr. 
Donaldson for his unfailing helpfulness and encouragement, 
and her appreciation to Dr. Stotsenburg and Dr. Heuser, and 
to the other members of The Wistar Institute who did much to 
aid in the course of the experiments which have extended over 
the past two years. 
