108 Methods in Plant Histology 



upon the objects. Dr. Land uses coarse wire gauze, cut into strips 

 about 15 mm. wide and tapered at both ends. The strip is then bent 

 so that the pointed ends rest upon the bottom of the No. 4 shell, 

 while the middle portion forms a flat table upon which the paraffin 

 may rest. Dip the wire gauze table into xylol and then slip it care- 

 fully into the No. 4 shell. The table portion should be 10 or 15 mm. 

 above the material, and there should be enough xylol to extend a few 

 millimeters above the table. Place on the table a block of paraffin 

 about equal to the volume of the xylol in the shell. The table not 

 only prevents the paraffin from injuring the material by mechanical 

 pressure, but insures considerable diffusion before the mixture of 

 paraffin and xylol reaches the specimens. After 24 hours (or several 

 days, if time permits) at room temperature, place the shell on a thin 

 piece of wood or corrugated paper on the top of the paraffin bath. 

 Do not place the shell directly upon the metal of the bath, since it 

 is better to minimize heat. As soon as the paraffin is dissolved, add 

 some more, this time leaving the cork out, in order that the xylol 

 may evaporate. About 24 hours on the top of the bath should be 



sufficient. 



THE PARAFFIN BATH 



This step is usually called infiltration, but when the transfer 

 from the clearing fluid to paraffin is made gradually, as has just been 

 indicated, the process of infiltration is already begun. It is now 

 necessary to get rid of the xylol or other clearing agent. This is 

 accomplished, to a considerable extent, by pouring off the mixture of 

 xylol and paraffin and replacing it with pure melted paraffin; but 

 some xylol remains in the tissues and must be removed. Do not put 

 the shell into the bath, but use a flat dish of some sort. The main 

 object is to have a fairly large surface exposed, so that the remaining 

 xylol may evaporate as rapidly as possible. Change the paraffin 

 two or three times. Soft paraffin (about 45 C.) may be used at 

 first, but the second should be the paraffin of the grade in which the 

 material is to be imbedded. If there are two baths, one should be 

 kept at 46 C. and the other at 53 C., if the material is to be imbedded 

 in 52 C. paraffin. While using the soft paraffin, keep the material 

 in the 46 C. bath; for the harder paraffin, use the 53 C. bath. 



