386 Introduction to Botany. 



this on page 374.) The jelly hardens on cooling and holds the cover- 

 glass firmly. After a few months the edge of the coverglass should be 

 cemented to the slip by a thick solution of shellac in 95 % alcohol, add- 

 ing to each 10 cubic centimeters of the solution 7 drops of castor oil. 



Imbedding in Paraffin. If material is to be imbedded in paraffin, 

 it must be passed from the 70% alcohol, or the mixture of alcohol, 

 glycerine, and water (see under Chrom-Acetic Fixative), through gradual 

 degrees of concentration into a solvent of paraffin, such as chloro- 

 form, and finally into pure paraffin having a melting point close to 

 52 C. Proceed as follows: From the 70% alcohol, or from the 

 alcohol, glycerine, and water mixture, transfer the material suc- 

 cessively to 80% alcohol, 95% alcohol, absolute alcohol, equal parts 

 of absolute alcohol and chloroform, pure chloroform, a second pure 

 chloroform, leaving it in each grade about 2 hours. Then transfer 

 the material to a vial, and pour over it enough chloroform to cover it, 

 but no more, and add a shaving of paraffin. Continue to add paraffin, 

 a little at a time, until no more can be dissolved at the room temper- 

 ature. Now place the vial on the copper plate of the paraffin bath 

 described below, with enough asbestos paper or felt paper between it 

 and the plate to keep it just below the melting point of pure paraffin, 

 and add a few more bits of paraffin to the vial. Leave the vial stand- 

 ing thus until the chloroform is entirely evaporated, which will be when 

 the paraffin no longer has a sweetish taste. If the paraffin should tend 

 to solidify while driving off the chloroform, remove some of the paper 

 separating the vial from the copper plate, for the paraffin should be 

 kept in a fluid state. Pour the material, paraffin and all, into the 

 dish of paraffin of the paraffin bath, and leave it there from 24 to 48 

 hours in order thoroughly to infiltrate the tissues with the paraffin. 

 Then pour the material and melted paraffin into a small paper tray, 

 made by turning up the edges of stiff writing paper for about half an 

 inch. Heat dissecting needles in a blue flame, and arrange the mate- 

 rial in orderly rows, leaving enough space between the pieces so that 

 each piece can be cut from the block with a good border of paraffin 

 about it. Now float the tray in a dish of cold water ; blow upon the 

 surface of the paraffin to harden it ; and submerge the tray as soon as 

 the surface film of paraffin can bear the weight of the water. In cut- 

 ting out a piece of paraffin with an object imbedded in it, preparatory 

 to mounting it on a microtome (see under Cutting and Mounting Paraf- 

 fin Sections), score the paraffin block deeply on both sides with a knife 



