OLFACTORY BULBS OF THE ALBINO RAT 245 
may work out. A count was first made of all cells at either end 
of the series and those in every tenth section through the middle 
portion. The result when computed was 95,993 mitral cells. 
Then the middle section of every ten was counted with a total 
result of 83,974 cells. Two other series were attempted but 
abandoned as the bulbs were so irregular that an accurate 
count would have required the enumeration of the cells of at 
least every alternate section. The other bulbs, except Cs 
for which every fifth section was counted, were fairly regular 
so that the mitral layer offered no such complications. For 
these, the method of counting all cells at either end of the series 
and those of every tenth section through the median portion 
was followed. The sequence of counts was varied with each 
bulb, and the records kept in various ways and not infrequent 
recounts made. The recounts were surprisingly close to the 
original, for, as has been stated, it is not always easy to decide 
whether or not a cell should be counted, and in focusing as one 
counts, a granule lying below or above a portion of a mitral 
cell sometimes looks very like a nucleus, but the error due to 
this cause is probably too small to be considered. 
Details of counts of the different bulbs, arranged in the order fol- 
lowed in table 3. 
Bulb X,, thirty day, initial control. Cross sections. Mitral cells 
counted in every section of anterior end back to the first section in 
which the mitral cells appeared in a single layer. From this point, 
counts were made for every tenth section back to the cerebrum. By 
computation, the total number of mitral cells was 64,775. By a 
recount in which the mitral cells of every other section were enumer- 
ated the computed number was 64,470 making a difference of only 
0.4 per cent in the two counts. The series of sections for the region 
beneath the cerebrum was incomplete, the posterior portion not having 
been preserved. A count was made, however, of the sections which 
were present. This number added to the number already counted 
by the second method, brought the total up to 71,914 cells. 
Bulb E,, Test, defective diet series. Sixty-two days. Sagittal 
sections. Mitral cells counted in all sections at either end of the series 
and for every tenth section between. 
Bulb C; Test, defective diet series. Fifty-nine days. Sagittal 
sections. Counts made as in F;. 
Bulb Q;, thirty day, initial control. Defective diet series. Cross 
sections. Mitral cells counted in allsections at both ends of the series. 
