224 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
2. Silver nitrate was treated with a 20% solution of formalin, at 
room temperature. ‘There was no evidence of chemical change. 
When heat was applied there was a deposit of metallic silver. 
3. Ammoniacal silver oxide solution, when treated with pyrogallic 
acid at room temperature, yielded a heavy precipitate of finely divided 
silver. 
4. Ammoniacal silver oxide solution, when treated with a solution 
of formaldehyde, immediately yielded a copious, heavy, somewhat 
spongy, precipitate of metallic silver, gray to black in color. 
On the basis of these tests then, it appears, that there are good 
chemical reasons for expecting Bielschowsky’s fluid to serve better 
than silver nitrate solution as a means of impregnating tissues with 
metallic silver, since it is much more readily reduced to the metallic 
state than is silver nitrate, whether the reducing agent be formaldehyde, 
or the developer used by photographers, and this at ordinary room 
temperature. The undesirability of leaving tissues for several days 
in the warm, non-preservative fluids required by Ramén y Cajal’s 
method is obvious. While all of the reagents used in developing 
photographic plates are strong reducing agents, formaldehyde, is 
sufficiently active for the purpose, and possesses the advantage that 
while it is acting as a reducing agent it is also acting as a preservative. 
The merit of any method, however, is determined by the results 
which it yields rather than by theoretical considerations. ‘The Ramén 
y Cajal process has many warm advocates. I tried it without success 
in this investigation, but have since secured excellent impregnation of 
nerve terminations by its use. 
My experience has been that success in impregnating the nerve 
terminals of the ear requires the use of a stronger solution of silver 
oxide and a longer treatment than is necessary for central organs. 
In order to arrive at once at a knowledge of the optimum conditions 
as to concentration and duration of treatment, I ran through a multiple 
series of ear sacs, varying the concentration of the Bielschowsky’s 
fluid and the duration of treatment by regular intervals. ‘The most 
satisfactory preparations proved to be those made from material which 
had remained for 30 to 45 minutes in a fluid prepared by adding to 
20 cc. of 2% silver nitrate solution 5 drops of a 40% solution of sodium 
hydroxide, and dissolving the precipitate of silver oxide thus formed 
in the smallest possible amount of ammonium hydroxide. 
Serial sections have been cut, in the usual way. ‘The most advan- 
tageous thickness has been found to be 10 mikra. Sections of that 
thickness are sufficiently transparent, and permit one to study a larger 
