Differential Staining Of Tissue In The Block With Picric Acid And The Feulgen Reaction

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Abstract
The authors have found a modification of the Feulgen reaction to be a satisfactory stain for tissue in the block. Pieces of fresh mammalian tissue not thicker than 5 mm. are fixed for approx. 48 hrs. at 25 [degree]C in a mixture of equal parts of 5% aqueous sulfosalicylic acid and satd. aqueous picric acid. They are washed for 30 min. in 3 ten-minute changes of dist. water and placed in Feulgen''s staining soln. diluted to 1/2 strength with dist. water. The staining soln. is allowed to act for 24 hrs. (2- to 3-mm.-thick blocks) up to 48 hrs. for 5 mm. thickness. After staining, the specimens are transferred to a mixture of Na bisulfite, 0.5 g. and N HC1, 5 ml. in 100 ml. of dist. water. Two changes of 15-30 min. each in the acid sulfite are given and these are followed by dehydration through 50%, 70% and 95%, in which the stained tissue is allowed to remain overnight. The dehydration is completed in 2 changes of abs. alcohol with subsequent clearing in xylene and embedding in paraffin. Sections may be cut 10 [mu] or other thickness desired, mounted on slides, paraffin removed, and covered in the usual manner. Nuclei stain reddish violet against a lemon yellow background when the stain is typical. Orange G, 200 mg. per 100 ml., may be added to the fixing fluid if a more polychromatic effect is desired.