OLFACTORY BULBS OF THE ALBINO RAT 243 
2. Size and number of mitral cells 
The cells of the mitral layer show a good deal of variation in 
size and shape and there is much difference in these respects in 
different regions of the same bulb. This makes the comparison 
of the size of the mitral cells in large and small bulbs rather 
difficult. 
But if all the mitral cells of a section from a small bulb are 
drawn with a high magnification by means of camera lucida or 
projection apparatus and those cells arranged side by side with 
a series from a corresponding section of a large bulb, drawn to 
the same scale, it is possible to make a general comparison. In 
this way the mitral cells have been compared, and there is no 
doubt I think that the mitral cells of large bulbs are larger and 
better developed than those of small bulbs. 
Details of technique and examination. It was sometimes quite 
difficult to determine whether a cell should be counted or not. 
For instance, when counting mitral cells it was hard to know 
at times whether a cell was a mitral cell or a brush cell, as many 
cells occur in the mitral layer which are exactly like those large 
cells occurring in the molecular layer but which lack the typical 
mitral form. On the other hand, typical mitral cells occur not 
infrequently out in the molecular layer or even among the 
granules on the inner edge of the glomerular layer. For this 
reason and in order that there might not be any unconscious 
influence in deciding whether cells should be counted, an at- 
tempt was made to vary the order of procedure for each successive 
count. 
A rather complete count was made of the mitral cells of four- 
teen bulbs and of the small cells of the gray layer in four bulbs. 
Eight of these were cut longitudinally and six cut transversely. 
The first series counted were those of X,, Initial control, 
Series E and X,, Test, Revolving Cage Series. In both series 
every other section was counted for the region anterior to the 
cerebrum—corresponding to the portions of these same bulbs 
in which the small cells of the gray layer had been counted. The 
result was 64,470 cells for X,, a 0.017 gram. thirty-day control 
