If the specimen to be cut is a leaf, a flower-petal, or other thin, flexible part of a plant, it may be placed between pieces of elder pith or slices of carrot or potato before cutting.
SHORT PARAFFIN PROCESS
In most cases, however, more perfect sections will be obtained if the specimens are embedded in paraffin, by the quick paraffin process, which is easily carried out.
After boiling the specimen in water, remove the excess of moisture from the outer surface with filter paper or wait until the water has evaporated. Next make a mould of stiff cardboard and pour melted paraffin (melting at 50 or 60 degrees) into the mould to a height of about one-half inch, when the paraffin has solidified. This may be hastened by floating it on cool or iced water instead of allowing it to cool at room temperature.
The specimens to be cut are now placed on the paraffin, with glue, if necessary, to hold them in position, and melted paraffin poured over the specimens until they are covered to a depth of about one-fourth of an inch. Cool on iced water, trim off the outer paraffin to the desired depth, and the Specimen will be in a condition suitable for cutting.
Good workable sections may be cut from specimens embedded by this quick paraffin method. After a little practice the entire process can be carried out in less than an hour. This method of preparing specimens for cutting will meet every need of the pharmacognosist.
LONG PARAFFIN PROCESS
In order to bring out the structure of the protoplast (living part of the cell), it will be necessary to begin with the living part of the plant and to use the long paraffin method or the collodion method.
Small fragments of a leaf, stem, or root-tip are placed in chromic-acid solution, acetic alcohol, picric acid, chromacetic acid, alcohol, etc., depending upon the nature of the specimen under observation. The object of placing the living specimen in such solutions is to kill the protoplast suddenly so that the parts of the cell will bear the same relationship to each other that they did in the living plant, and to fix the parts so killed.
After the fixing process is complete, the specimen is freed of the fixing agent by washing in water. From the water-bath the specimens are transferred successively to 10, 20, 40, 60, 70, 80, 90, and finally 100 per cent alcohol. In this 100 per cent alcohol-bath the last traces of moisture are removed. The length of time required to leave the specimens in the different percentages of alcohols varies from a few minutes to twenty-four hours, depending upon the size and the nature of the specimen.