FUNDAMENTAL CONSIDERATIONS 
25 
The acetic acid in all of the Flemming fluids is of great advantage 
since it penetrates very rapidly, carrying the chromic acid or chromic 
and osmic acids into the tissue depths, thus insuring complete 
fixation. 
The material to be fixed should be cut into small pieces not longer 
than 5 mm. nor broader than 2 or 3 mm. The amount of fixation 
to be used should not be less than 15 times the bulk of the material 
to be fixed. The material should be placed in the fixing fluid im¬ 
mediately after it is gathered. One or two drachm homepathic 
phials are convenient for the process. The material is kept in the 
fixing fluid for from 12 to 24 hours and then washed in small cheese 
cloth bags which are placed in running tap water for from 6 to 12 
hours or over night. 
Dehydrating and Hardening. —After washing the material, still 
kept in the bags, is placed in 10 per cent, alcohol for 1 hour and is 
then carried through a series of alcohols. Each of the series 10 
per cent stronger than the one before it, remaining in each grade for 
1 to 2 hours until 70 per cent, alcohol is reached. Take out of 
bag and place in phial in 70 per cent, alcohol. If the material is 
not to be imbedded in paraffine immediately, it can remain in 70 per 
cent, or 85 per cent, alcohol (if very delicate) until needed. It is 
not safe to leave very valuable material in a grade below 70 per cent, 
over night. From the 70 per cent, alcohol it is carried to 85 per 
cent, to 95 per cent, to absolute alcohol, remaining in each at least 
6 hours with 2 or 3 changes of the last. 
Clearing and Imbedding. —In order to get the material from ab¬ 
solute alcohol into paraffine, some medium must be used which mixes 
with absolute alcohol and which also dissolves paraffine. Either oils 
such as cedar, clove or bergamot or substances like xylol, chloroform 
or benzol satisfy this requirement. To clear with xylol—transfer 
material from absolute alcohol to a mixture of % absolute alcohol and 
M xylol for 12 hours, then to mixture of equal parts of absolute 
alcohol and xylol for 12 hours, then to % xylol and absolute 
alcohol for 12 hours to pure xylol for 12 hours. To phial containing 
material in pure xylol add paraffine in small pieces and put on top of 
paraffine bath sufficiently long until paraffine is melted. Then add 
more paraffine and put phial in paraffine bath at]56°C. over night. 
