GO Paraffin Method (chap. 5) 



of tissue parts. A safe temperature is approximately 5-10°C lower than 

 the melting point of the paraffin. When the sections are spread smooth, 

 the excess water may be drained off; this is facilitated by touching a 

 piece of cleansing tissue or filter paper to the edge of the slide and 

 around the sections. Permit slides to dry overnight on the warm plate 

 or in an oven of comparable temperature. If they must be stained on 

 the same day as they are moimted, dry them in one of the mechanical 

 hot air dryers (Technicon or Lipshaiu Companies). 



Certain tissues frequently develop cracks through the sections while 

 drying — an aggravation common to spleen, liver, lymph nodes and 

 nervous tissue. To prevent this, as soon as the sections are spread, drain 

 and blot them free of as much water as possible and dry them at a 

 higher temperature (60-65°) or in the mechanical hot-air dryer. 



Properly mounted sections will have a smooth, almost clear appear- 

 ance. If they have a creamy, opaque texture, and when examined from 

 the tindersurface reflect light, air is caught between the glass and sec- 

 tions. Such tissues will float off in aqueous solutions. The cause usually 

 lies either in poorly cleaned slides or in drying at too low a temperature 

 or not long enough. If, when motinting, an excess of bubbles appear 

 under the sections, tise distilled water which has been boiled for some 

 time to release trapped air. Poorly infiltrated sections and nervous tis- 

 sue which has been soaked in water usually fail to adhere; these can 

 possibly be saved by the following method. 



Because of their tendency to loosen from slides, certain types of tis- 

 sues may require special treatment. These tissues include brittle sec- 

 tions, tissues containing a large amotnit of yolk or osmic acid, and 

 sections which will be subjected to strong acids or alkalis during stain- 

 ing (as well as the poorly infiltrated sections and nervous tissue men- 

 tioned above). After drying, and when ready to stain, dissolve out the 

 paraffin with toluene or xylene. Place the preparations for 1-2 minutes 

 in absolute ethyl alchohol, followed by 1-2 mintues in a dilute solution 

 (about 0.5%) of nitrocellulose in ether-absolute alcohol (50:50). Drain 

 off excess nitrocellulose, but do not allo^v it to completely dry; wave 

 slide in air a second and place it in 70% or 80% alcohol. Continue with 

 the planned staining method. 



Serial Sections 



With a few exceptions, the usual paraffin method is used for serial sec- 

 tions, and in most cases, every section is mounted and in correct order. 

 While sectioning, the ribbons are arranoed in a cardboard box from 



