Chapter W 



Staining 

 Procedures 



Usually certain standard principles apply to the processing of tissue 

 on slides, but many exceptions and variations occur and Avill have to be 

 handled individually. 



The sections first must be deparaffinized, because most stains are 

 applied in either aqueous or alcoholic solutions and would not pene- 

 trate efficiently through paraffin-infiltrated tissues. The customary sol- 

 vent for paraffin is xylene. This is followed by the removal of the xylene 

 with absolute alcohol because stains rarely can be applied successfully 

 in a xylene medium. After the removal of the xylene, a general rule is 

 to transfer the slides to a medium comparable to the solvent of the dye 

 being used. That is, if the dye is a waiter solution, the slides are hydrated 

 through a series of decreasing alcoholic and increasing aqueous dilu- 

 tions, such as 95%, 80%, 70% and 50% alcohol, or the like, and 

 finally they go into water. If the dye is dissolved in a 50% alcoholic 

 solution, then the slides are carried only to 50% alcohol before going 

 into the staining solution. 



During the hydration process, undesirable pigments or other ma- 

 terials (mercuric chloride crystals, formalin pigment, etc.) are removed 

 and the slides washed well to remove the responsible reagent. Counter- 

 stains (background color) or other special treatments must be applied 

 in their proper sequence, to allo^v each dye or chemical to maintain its 

 specific effect on the tissue elements. Improper sequence of staining, 



114 



