MAUTHNER’S CELL 89 
content of the brains, thus reducing the shrinkage of the cells 
without materially injuring the impregnation. This variation of 
acetic acid may be from 5 to 10 per cent. Larval Ameiurus and 
Salmo gave the best results with this mixture: 
Absolute alcohol 10 parts 
Glacial acetic acid 1 part 
For adult Ameiurus both of the following fixing fluids gave 
good results in many cases: 
Absolute alcohol 19 parts 
Glacial acetic acid 1 part 
or 
Absolute alcohol 19 parts 
Glacial acetic acid 2 parts 
Chloroform 10 parts 
Twenty minutes is usually sufficient for fixation, though the 
brains may be left for 13 hours without becoming too brittle to 
cut. They are then rinsed in 80 per cent alcohol followed by 
distilled water and placed in a solution of silver nitrate. The 
penetration of the silver is the most important factor and this 
is facilitated by changing the strength of the solution daily and 
by keeping the material in an incubator. The material is put 
into 0.5 per cent silver nitrate and kept in the dark at a tempera- 
ture of 35 to 40°C. for 24 hours, then washed in distilled water 
5 minutes and put into a 1 per cent solution of silver nitrate. - 
On the following day this is again changed to a 1.5 per cent solu- 
tion, then to 2 per cent, then back to 1 per cent and the process 
repeated. The silver bath should not be stronger than 2 per 
cent, and the silver treatment should last not less than 3 days 
nor more than 8 days. Cells and their processes are usually best 
shown in preparations left in the silver for from 4 to 5 days, 
but in any case the material must be brown at the end of this 
treatment. It is then rinsed in distilled water and developed for 
from 12 to 24 hours in a 1 per cent solution of pyrogallol in 5 
per cent neutral formol. It is then rinsed in distilled water, fol- 
lowed by 50 per cent alcohol, rapidly dehydrated in two changes 
of 95 per cent alcohol and of absolute alcohol, cleared in cedar 
