1. Small bits of fresh tissue, or tissue fixed in formol, in water-free acetone over copper sulphate for ½-1½ hours.
2. Transfer tissue directly to fluid paraffin in the oven for ½-1½ hours; the acetone evaporates, and the tissue is infiltrated with paraffin; or put into xylol 5-10 minutes, then in paraffin 15-20 minutes.
3. Block.
By this method the entire process of fixing, hardening, imbedding, cutting and staining can be carried out in half an hour, and by it the freezing-microtome can be dispensed with in a large part of quick diagnostic work.
Pyridin Method.
1. Fix in formol.
2. Dehydrate and clear in pyridin.
3. Paraffin.
This method requires a longer time than the acetone method, and is not so good.
Combinations of celloidin and paraffin may be employed by imbedding first in celloidin, transferring block to origanum oil, then xylol and finally paraffin. Formol-agar has been recommended by Bolton and Harris for simultaneous fixation and imbedding. It offers no especial advantages. Wright uses formol-gelatin for imbedding tissues for sectioning on the freezing microtome. The bits of tissue are placed in warm 20 per cent pure gelatin; this is allowed to set, and the block placed in 10 per cent formol for 24 hours; it is then frozen and cut. Soap-gelatin, glycerin-gelatin, gum-glycerin, etc., are now rarely used for imbedding.