The Paraffin Method 109 



Do not throw away the paraffin which you pour off, but put it in a 

 waste jar or beaker, or, still better, in a small tin larci pail, in which 

 you have made a lip to facilitate pouring. This can be placed in the 

 bath, or, in winter, on the radiator, and the xylol will gradually 

 evaporate. After long heating, the paraffin not only becomes as 

 good as new, but even better, since it becomes more homogeneous 

 and tenacious. If it contains dust or debris of any kind, it may be 

 filtered with a hot filter. 



The time required varies with the character of the material and 

 the thoroughness of the dehydrating and clearing. If this schedule 

 has been followed up to this point, the time will be much shorter than 

 most investigators now deem necessary. Fern prothallia infiltrate 

 perfectly in 15 to 20 minutes; onion root-tips in 20 to 30 minutes; 

 ovaries of Lilium at the fertilization stage, 30 to 40 minutes; 5 or 

 6 mm. cubes of endosperm of cycads, containing archegonia, 1 hour 

 to H hours; median longitudinal sections, 4 or 5 mm. thick, through 

 ovulate cones of Pimis Banksiana ma}' require 6 or 8 hours; if serial 

 sections through the entire cone are wanted, Miss Aase found that 

 the time must be prolonged to 24 or even 48 hours. When one is 

 dealing with many lots of the same kind of material, as in research 

 work, the time required for infiltration is easily determined. As a 

 rule, minimize heat. It is, probably, never necessary to use paraffin 

 with a melting-point higher than 52 C. With Land's cooling device 

 sections 1 p, in thickness can be cut from 52 C. paraffin; and sections 

 2 or 3 IJL in thickness can be cut from 45 C. paraffin. 



IMBEDDING 



Material may be imbedded in paper trays, Petri dishes, watch 

 crystals, or in apparatus made for the purpose. Many use imbedding 

 L's consisting of two L-shaped pieces of brass or type metal. A pair 

 of L-shaped pieces with arms three inches long will furnish a box of 

 almost any required size. A piece of glass serves for a bottom. The 

 most satisfactory imbedding-dish we have used is a thin rectangular 

 porcelain dish, glazed inside. This dish, called a Verbrennungsschale, 

 is made by the Konigiiche Porzellan-Manufactur, Berlin, Germany. 

 The most convenient sizes are 40X50X10 mm., 68X45X10 mm., 



