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 i 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 

 ij^ 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 

 y xylol for 12 hours, then to mixture of equal parts of absolute 

 alcohol and xylol for 12 hours, then to % xylol and J^ 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 56C. over night. 



