236 CAROLINE M. HOLT 
suited to comparative study of the size of bulb elements. Ac- 
cordingly, the method was further tested, and at the same time 
an examination was made of the effect of Miiller’s fluid and of 
Orth’s Formol-Miiller solution upon the various parts of the 
brain. 
A long series of experiments demonstrated quite conclusively 
the following points which have an important pean ae upon the 
present investigation. 
1. Of the three fixing fluids tested, Ohlmacher’s solution causes 
the least change in weight in brain tissue. 
2. Orth’s solution (cold) causes a slight increase in weight. 
3. Miiller’s solution causes a very considerable increase in 
the weight of brain tissue as has already been noted (Donaldson, 
’94). 
4. Olfactory bulbs, fixed in Ohlmacher’s solution, reach a 
state of equilibrium at the end of twenty-four hours; fixed in 
Formol-Miiller, they reach this state at about the end of one 
week; fixed in Miiller’s solution alone, changes continue from 
six weeks to two months. 
5. There seems to be no appreciable individual variation in 
the reactions of albino rat brains of like age to Ohlmacher’s 
solution, to Miiller’s fluid, or to the Formol-Miiller solution. 
The results obtained by Dr. King are due apparently to the 
fact that the brains which were weighed in her experiments had 
been fixed for varying short lengths of time and the initial changes 
in weight were so rapid that there appeared to be a considerable 
difference in the way the various brains reacted to the fixative, 
when in reality, had all the brains been fixed for exactly the same 
length of time, no such large disagreement would have been 
found. 
ll. THE PROBLEM OF SIZE DIFFERENCES 
Although under normal conditions, there is a good deal of 
variation in the size of the olfactory bulb of the albino rat, 
we have found that it is possible, experimentally, to increase 
this range of variation to a very considerable degree. The 
question next arises as to the structural cause of the difference 
