OLFACTORY BULBS OF THE ALBINO RAT 249 
M;, and Xs. Bulb X, was too incomplete to make such caleula- 
tion possible. Let us take M,. The small cells were counted 
back to section 4, 1/1. We have the total number of mitral 
cells and also the number of mitral cells back to section 4, 1/1. 
This gives us the data for computing the total number of small 
cells as follows: 
MuatralaceliisroteVicntorse ction Axailt/ilmee ce 2). l aeeene ene hens a Ser ue ne 50,729 
Mota lemantralecelillistaec sisters Mets Ue tiat ios lake cea eetee PRAY «cure uel do. 76,611 
66 per cent of mitral cells in anterior portion. 
NumibenusmiealllcellsSitomsectiomed lll se ae ee ee eer 662,982 
If this number equals 66 per cent of the total number, then the total number 
of small cells in the gray layer would be 1,004,518. 
If we treat M; in the same way we have: 
IMGnaesll- Cabls tro. SeCunom 3), GPs 8025 ne deee can tossosndencectoaene BURUUO 
MO uallenmitraleCellllister teat weet tens sine Misntn on sic Soe SR eNn eon geet oop Sears 76,595 
73 per cent of mitral cells in anterior portion. 
Niumberssmallizcelliss torsectlomes- 16/12... see see ees ae eee 716,382 
Rhenyiotalenumlyerssnialllecelllichesere iss sels ee eee, eee 981,619 
According to this computation the test bulb would have two per cent more 
cells than the control. 
Now if we treat X, in like manner we have the following: 
Mitral celiiskionsecinonko sll pane eee ene eee ee 27000) 
Mo tallenniGrealecelll Sis settee wae ee kG AS cae a ee Oa Te Hd, 80,114 
77 per cent of mitral cells in anterior portion. 
Suigllll Calle wo, SECO IY Gee oles cea tle boss he satan seen 789,680 
{lever THON aayoramloere our Siooellll Celle occ one eomenebocbumeoncocuce 1,020,258 
These total numbers are strikingly close. The number of 
bulbs is too small to warrant us in drawing general conclusions 
but I think the results certainly point to close agreement in 
number even of the small cell elements in the gray layer. 
While there is a constant increase in the number of myelinated 
fibers correlated with age, as has been demonstrated by Green- 
man (713) for the peroneal nerve, Boughton (’06) for the oculo- 
motor, Hatai (02) and (’03) for both dorsal and ventral roots 
of several spinal nerves, and Dunn (12) for the ventral root of 
the second cervical nerve; there is very little evidence of any 
true increase in the number of cells in the central nervous system 
after the first few days after birth. Allen (’12) found dividing 
cells in the cerebellum up to twenty-five days and in the cere- 
brum up to twenty days, with a few along the lateral walls of 
THE JOURNAL OF COMPARATIVE NEUROLOGY, VOL. 27, NO. 2 
