OLFACTORY BULBS OF THE ALBINO RAT 239 
weighed, was 0.020 gram—the approximate weight then of the bulb 
shown in the drawing. Figure 2, plate 1, is a median sagittal sec- 
tion through the control bulb. The rat from which this was taken 
was 166 mm. long, with brain weight of 1.698 grams, and the 
weight of the corresponding bulb was 0.032 gram. Like the bulbs 
of very young rats, the gray layer of the stunted bulbs extends 
somewhat further, in proportion, beneath the cerebrum than in 
the case of normal older individuals. 
When the stunted bulb is compared with its control, there 
appears to be a rather uniform size difference involving all parts 
of the bulb. It is hard to compare the outer fiber layers owing 
to the difficulty in removing the bulbs perfectly from the skull. 
The anterior end of the fiber layer is very likely to be entirely 
torn away and sometimes the ventral side also suffers. However, 
it is plain that the glomeruli of the larger bulb are much larger 
and more open; the granular cells are not so closely packed to- 
gether; and the gray layer is usually broader in the larger bulb 
and the inner granular area considerably more extensive. These 
differences between the peripheral portions are illustrated by 
the more highly magnified mid-dorsal areas S and S of figures 1 
and 2, shown in figures 3 and 4 of plate 2. 
Plate 3 shows three cross sections; through Q;, a thirty-day 
control bulb (fig. 5); M,, a sixty-two-day stunted bulb (fig. 6); 
and M;, the sixty-two-day normal control (fig. 7), for M,. These 
sections were made through the region where the bulbs are 
usually cut from the brain. The figures illustrate another 
typical difference. The normal bulb (figs. 5 and 7), as it grows, 
elongates more rapidly than it increases in thickness and it 
tends to grow faster dorso-ventrally rather than laterally. In 
these figures, the outer fiber layer is probably complete at the 
sides. Ventrally it has doubtless been torn away to some extent 
in all three bulbs. The difference in size of the glomeruli is 
well shown here, but while there is a greater area of gray matter 
in figure 7 than in the other two, the gray layer seems narrower 
than in M, (fig. 6). The companion bulb of Q,;, (fig. 5) weighed 
0.024 gram, that of Mg, (fig. 6), 0.025 gram while M; weighed 
0.037 gram (fig. 7). The portion of Q; anterior to the section 
