OLFACTORY BULBS OF THE ALBINO RAT 237 
in size. Is it one of size of elements or of their number? Have 
we more cells and fibers in the heavier bulb or are the cells and 
fibers merely of a larger size? The present paper deals only 
with the question of cells. The fibers have yet to be examined. 
Ill. TECHNIQUE AND METHODS OF STUDY 
Since experiments on the effect upon the rat brain, of Ohl- 
macher’s, Miiller’s, and the Formol-Miiller solutions have demon- 
strated that for brains of like ages there is a definite, practically 
unvaried, swelling or shrinking reaction for any given fluid, 
the brains of the rats used in the defective diet and exercise 
experiments were fixed in these several solutions for histological 
comparison. For the present cell study the method adopted was 
that recommended by King (’10) for study of the cortex, namely 
fixation in Ohlmacher’s solution for twenty-four hours, followed 
by one hour in 85 per cent alcohol, three to four days in iodized 
70 per cent alcohol, double embedding in celloidin and paraffin, 
and staining in carbol-thionin and eosin. However, after the 
first trials, this method was varied in the matter of embedding. 
For such small objects as the olfactory bulbs, paraffin proved 
more satisfactory when used alone. Sections were cut 8yu 
thick and mounted serially. A rather deep thionin stain gave 
the best results for cell enumeration. 
1. Preparation of sections 
At first, some bulbs were cut sagittally and the largest sections 
compared. In the study of these sections the number of cells 
in the gray layer of the different bulbs was found to be so nearly 
identical that it was decided to attempt a thorough study of cell 
number. 
In dissecting a rat brain into its parts, the bulbs are cut from 
the brain in such a way as to leave an appreciable portion of the 
bulb attached to the cerebrum. The method followed was to 
place the brain, ventral side down, on a flat surface and with a 
knife held in a plane perpendicular to the table, to sever the bulb 
at the point where it disappears beneath the cerebrum (plate 1). 
