PART II. ON THE NUMBER OF NERVE CELLS IN 
LARGE AND SMALL OLFACTORY BULBS 
CONTENTS 
1. Introduction. Preliminary experiments on the effect of certain fixa- 
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lieeihe problem, Of size diterences2y5 2: H..¢4). Lag eet eis th oak 236 
iieehechniqte-and methods or study... 2j5..5. bck eter eee ela bate 237 
IPE Te pArablONyOlSCCMOMS 2:2... asa ae Te ear es Ate cata 237 
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iiVerGeneral differences in sizes) ts 7.4. 425.02 ee ih See Ath Ate Ry Sa 238 
Vie Comparison: of .cells:of ray layer n...cosee eee ee gees es 240 
1. Size and number of small cells in molecular layer................ 240 
Je Size and miimper or misral cells. scat te oo se ee ee ce oe t,o 243 
3. Study of the small cells in the gray layer............ Pod Cs aE te 248 
Nile (Conclusions soe a ed. |. UR Re: WR DR ott Sete dees 250 
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I. INTRODUCTION 
The foregoing studies have shown that it is possible to change 
the relative weight of the olfactory bulbs in the albino rat 
(Holt, ’17). This relative weight is decreased by a defective diet 
and increased by exercise. Such being the case, it seemed very 
desirable to make a histological comparison of the bulbs which 
had been stunted by a defective diet or enlarged by exercise, with 
those of rats reared under normal colony conditions. For this 
purpose it was of course essential to find a method of fixation and 
treatment which would give uniform results. Fixation in Ohl- 
macher’s solution as recommended by King (’10) for the study of 
cortex cells, gave very satisfactory results, but her statement that 
“various individuals react differently although subjected to the 
same course of treatment,” and her tables (loc. cit., p. 231) 
showing a variation in shrinkage ranging from 2 to 18 per cent 
in brains so fixed, suggested that it would be best to examine 
this method a little more in detail. Unless uniform results 
could be obtained by it, this method would, of course, be un- 
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