242 CAROLINE M. HOLT 
TABLE 2 
BULB AGE HISTORY BRAIN WEIGHT |WEIGHT 1 BULB Ae eae 
days grams grams 
Dla Abe 30 | Control 1.338 0.017 636,656 
NERS: 62 | Underfed 31 days 1.461 0.025 662,982 
Gi... 62 | Underfed 31 days 1.543 0.027 601,982 
Gerace 61 | Normal control 1.630 0.031 675,305 
Mcgee 62 | Normal control Peale 0.037 716,582 
X,5....| 184 | Revolving cage 104 days 1.927 0.040 789,680 
number is one of the factors in bulb size. But corresponding 
sagittal sections had given fairly close agreement in numbers 
and the study of sagittal sections made it more and more evident 
that these counts of cross sections could be taken only to compare 
the parts commonly considered the bulb and not for an enumera- 
tion of the cells in the whole bulb. The difference in shape in 
the large and small bulbs made it apparent that a true count 
must be made either from sagittal sections or from cross sections 
cut through the entire length of the gray matter covering the 
bulb. Comparison of such sections as figures 1 and 2 made 
it clear that if we had, in reality, a constant number of cells in 
the gray layer, the numbers in the regions here designated as 
the ‘bulb’ could scarcely be expected to show any closer agreement 
than we find in this table, and would probably have the relations 
there given. For the larger and better developed the bulb, 
the greater the proportion. of it lying anterior to the cerebrum, 
while the young or the stunted bulb runs somewhat further back 
beneath the hemisphere and so some of the cells escaped enumera- 
tion. For example, M;, a bulb of 0.037 gram, has 271 sections 
containing mitral cells in the portion of the bulb beneath the 
cerebrum. Mg, the test bulb of this litter, which weighed but 
0.025 gram had 336 sections in this region. Taking these facts 
into consideration, the table in question pointed to a uniformity 
rather than variation in numbers corresponding to size. Later 
we shall see how, in the light of the study of the mitral layer, 
a part of this table can be shown to closely conform to this 
supposition that the number of cells in the entire gray layer is 
approximately constant for olfactory bulbs of different sizes. 
