OLFACTORY BULBS OF THE ALBINO RAT 205 
ceased to grow simultaneously with the body, while the cord 
increased somewhat in weight during underfeeding. 
Although there are, at present, no data by which it is possible 
to make a definite comparison between the effect of a defective 
diet and that of an adequate, but quantitatively insufficient 
diet, it is important to bear in mind in each case the method by 
which growth has been retarded or arrested. 
Two series of experiments upon the effect of underfeeding 
were undertaken—one upon rats which had been reared to the 
time of weaning (at three or at four weeks of age) by well-fed 
mothers, Series A; the other, upon rats reared to the time of 
weaning by underfed mothers, which meant rats underfed 
practically from birth, Series B. 
Observations were also made upon a few sick animals, Series C. 
2. Series A. Ax, rats underfed from time of weaning at eighteen 
to twenty days, and A», at thirty to thirty-two days 
a. Method. As has been previously stated, while there is a 
considerable range of variation between litters in the matter of 
the relative size of the olfactory bulbs, yet within a given litter 
the size is fairly uniform. For this reason, so far as possible, 
control and test animals were taken from the same litter. This, 
of course, made it necessary to select fairly large litters in order 
to have several animals for initial and final controls, and also 
for experiment. The litters were always taken from healthy 
stock animals. 
For the first few individuals experimented upon, no initial 
controls were examined, but the results of these experiments 
made the advisability of such controls apparent and subsequently 
each litter was weighed and divided into three groups; so far as 
possible, equivalent in sex, weight, and bodily condition. All 
these rats were ear marked and a card filed for the data upon 
each animal. 
The first or initial control animals were at once etherized, 
weighed, measured, eviscerated, and the brains removed. One 
olfactory bulb was cut off from each brain, in the following man- 
