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. [Illustration: 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. [Illustration: 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. HAND MICROTOME In cutting sections by a =hand microtome=, it is necessary to place the specimen, embedded in paraffin or held between pieces of elder pith, carrot, or potato, over the second joints of the fingers, then press the first joints firmly upon the specimen with the thumb pressed against it. If they are correctly held, the specimens will be just above the level of the finger and the end of the thumb, and the joint will be below the level of the finger. [Illustration: FIG. 33.--Hand Microtome] Hold the section cutter (Fig. 33) firmly in the hand with the flat surface next to the specimen. While cutting the section, press your arm firmly against your chest, and bend the wrist nearly at right angles to the arm. Push the cutting edge of the microtome toward the body and through the specimen in such a way as to secure as thin a section as possible. Do not expect to obtain nice, thin sections during the first or second trials, but continued practice will enable one to become quite efficient in cutting sections in this manner.