SECTION TWO 



6. Rinse briefly in cold N/i HCl. 



7. Rinse in distilled water. 



8. Immerse in solution A for half to one hour. 



9. Drain oflt excess fluid from slides; then rinse with three 

 changes of solution B. 



10. Wash well in running tap water. 



11. Counterstain in the fast green solution for about thirty 

 seconds. 



12. Dehydrate through the usual graded alcohols. 



13. Clear in xylol. 



14. Mount in D.P.X. 



Results: 



DNA is seen in shades of reddish purple against a blue-green 

 background. 



Notes: 



(a) Many other fixatives may be used instead of Zenker, but 

 the time required for hydrolysis (step 5) varies with diff'erent 

 fixatives. The following is a list of some of the fixatives stipulated 

 by Bauer (1933), with times, expressed in minutes, for hydrolysis: 



Bouiti is not recommended 



(b) Feulgen's reaction is based on mild acid hydrolysis of 

 deoxyribofuranose, which is the carbohydrate component of 

 DNA, to release aldehyde groups, which then unite with Schiff's 

 reagent to give a coloured product. 



(c) Schiff reagent, following Feulgen hydrolysis, is generally 

 believed to be specific for DNA. 



{d) Basic fuchsin is a basic dye of the triphenylmethane group. 

 It is the parent substance of a range of dyes varying in shade from 

 red through purple to violet and blue, according to the number of 

 methyl or ethyl groups added to the molecule of the original dye. 



401 



