Fig. 31.—Paraffin-embedding Oven
After dehydration the specimen is placed in a clearing agent—chloroform or xylol—both of which are suitable when embedding in paraffin. The clearing agents replace the alcohol in the cells, and at the same time render the tissues transparent. From the clearing agent the specimen is placed in a weak solution of paraffin, dissolved xylol, or chloroform. The strength of the paraffin solution is gradually increased until it consists of pure paraffin. The temperature of the paraffin-embedding oven (Fig. 31) should not be much higher than the melting-point of the paraffin.
The specimen is now ready to be embedded. First make a mould of cardboard or a lead-embedding frame (Fig. 32), melt the paraffin, and then place the specimen in a manner that will facilitate cutting. Remove the excess of paraffin and cut when desired.
Fig. 32.—Paraffin Blocks
In using the collodion method for embedding fibrous specimens, as wood, bark, roots, etc., the specimen is first fixed with picric acid, washed with water, cleared in ether-alcohol, embedded successively in two, five, and twelve per cent ether-alcohol collodion solution, and finally embedded in a pure collodion bath.
CUTTING SECTIONS
Specimens prepared as described above may be cut with a hand microtome or a machine microtome.