STAINING, PRACTICAL AND THEORETICAL 



6. Embed in 20% gelatine and leave to set. 



7. Cut out blocks of tissue and immerse them in formalin for 

 twenty-four hours. 



Note: The blocks may be stored indefinitely in this formalin 

 solution if desired. 



8. Rinse blocks in water and trim. 



9. Freeze blocks thoroughly until they are uniformly white. 



10. Allow the block to thaw somewhat until the knife cuts 

 easily. 



11. Cut sections up to 5/f in thickness and float onto slides with 

 distilled water. 



12. Drain off excess water and float sections on slides with two 

 or three drops of 1% gelatine. 



13. Drain off excess 1% gelatine and leave the slides in an oven 

 at 37° C. until the sections are dry. 



14. Immerse slide in 10% formalin for ten minutes to fix the 

 gelatine; then stain in the usual manner with Sudan 3, or Scarlet 

 R, Nile blue or osmic acid, or store the slides in the 10% formalin 

 until required. 



LOW VISCOSITY NITROCELLULOSE (L.V.N.) 



For embedding tissues 



Chesterman and Leach's technique using Low Viscosity Nitro- 

 cellulose (L.V.N.) offers advantages over the older method of em- 

 bedding in Celloidin, in that penetration is quicker, considerably 

 thinner sections can be cut, it is easier to use and considerably 

 cheaper than Celloidin. With L.V.N, technique large blocks, such 

 as half a cat's brain, can be cut at 15//; small blocks 5x5 mm., 

 can be cut at 5 to 7/^ on a paraffin microtome without any special 

 modification or attachment. 



L.V.N, is supplied damped with normal butyl alcohol; it is 

 more explosive than Celloidin and it should be handled with care. 

 When dry it will explode if hit. Exposure to sunlight should be 

 avoided. 



494 



