72 



Nilroccllulose Melhod (chap. 7) 



Embedding 



Slow Method 



Place the tissue in a small glass-covered dish (slender dish), and over it 

 pour 33-35% nitrocellulose luitil it is ^ to ^ inch above the tissue. Over 

 this pour a thin layer of ether-alcohol (1:1). Cover the dish tightly, and 

 allow to evaporate slowly until a proper consistency. If bubbles appear 

 in the medium, evaporation is proceeding too rapidy. A little Vaseline 

 on the ground-glass edge of the cover Avill help to seal it more tightly; 

 in dry, warm weather it may be necessary to enclose the evaporation 

 dish in another dish or jar to slow down the removal of solvent. The 

 process should take several days to a week or more, the slower the bet- 

 ter. Do not allow the medimn to become too hard; it should reach the 

 consistency of hard rubber and should feel dry and not show finger 

 prints. If a tough film forms quickly on the surface of the solution and 

 sticks to the side of the dish, carefully loosen the film from the glass to 

 alloAv more efficient evaporation. 



^Vhen the nitrocellulose is properly formed, trim it down to cutting 

 size, and moimt it on a fiber or wooden block. (Figs. 18, 19, 20, 21.) 

 Aroiuid the block, tightly ^vrap a band of hard bond paper, then secure 

 the band with string or stick it down with a paper label. (Do not use a 

 rubber band.) The paper must project high enough above the mount- 

 ing block to enclose the tissue block. Moisten the mounting block and 

 paper with ether-alcohol, then place a small amoinit of 33-35% nitro- 

 cellulose in the container formed by the two. Roughen the underside 

 of the tissue block with a needle, and cover it with a drop or t^vo of 

 ether-alcohol. Press the roughened surface tightly into the nitrocellulose 

 on the paper-wrapped block. After a few minutes in the air, place the 

 block in a closely capped jar with a small amoinit of chloroform; leave 

 it there 20-30 minutes. Add more chloroform to immerse the entire 

 block, and if possible allow it to "set" in chloroform overnight. There 

 are other and more haphazard ways of mounting nitrocellulose blocks, 

 but the above method is relatively sure. 



Romeis [1948) claims that if ^vooden blocks are used they should be 

 pre-seasoned with nitrocellulose. Cook them in distilled water, then 

 allo\v them to dry for several days. Extract with ecjual parts of 70% 

 alcohol and glycerine for a day, and wash the blocks in distilled water 

 until shaking no longer causes a foam. Cover the surface with 8% nitro- 

 cellulose, dry, and put the blocks in a glass bottle. 



