In this article we will discuss about the preparation of paraffin block.
Transfer the tube or tubes containing the material to a high temperature paraffin bath (60°C), along with some paraffin of suitable melting point taken in a beaker.
Suitable melting point refers to the melting point of paraffin which will give ideal ribbons of sections (see section cutting). This has to be learnt by experience. In India, 56-58°C paraffin is suitable for summer and 52-53°C paraffin for winter. In other seasons, a mixture of the two proves convenient.
When paraffin of both the tube and the beaker melts, pour off the supernatant paraffin of the tube and add some fresh paraffin from the beaker. Repeat the process 2-3 times at ½hr intervals till the smell of chloroform is completely removed.
Prepare a paper-tray as shown in Fig. 3.2. Place it on a rectangular glass plate. By using a glass plate the lower surface of the block is made smooth; it also makes the removal of the block easier. Keep a burner nearby and make a needle and a scalpel sufficiently hot. Pour some paraffin from the beaker into the paper tray.
The depth of paraffin need not be more than 1 cm. Take out the tube, stir it well and pour down the contents into the paper tray in one action so that all the buds or root-tips fall into it. Take the needle and the scalpel and with these arrange the buds or root-tips in straight lines as shown in Fig. 3.3. The materials are arranged in groups of 2 or 3. In case of root-tips, care must be taken to keep the tips at the same level.
Preparation of good blocks requires experience. The whole operation has to be completed very swiftly, as the upper layer of paraffin solidifies quickly in contact with cool air. To prevent this the hot scalpel is to be regularly rotated in the paper tray.
When paraffin starts solidifying around the needle and the scalpel, they are again heated. If all the material cannot be arranged in line, the excess is stored at one comer. This can be subsequently cut out and recast.