/. Staining Paraffin Sections 



This chapter is not intended to be a comprehensive treatise on 

 the theory and practice of staining. Historical reviews of the evokition 

 of biological staining and critical discussions of the chemistry of 

 dyes and of staining will be found in Conn's Biological Stains (1936) . 

 For our purposes it is a safe practical assumption that the staining 

 of cellular structures is based on specific affinity between certain dyes 

 and particular cell structures. This specificity is aided in some proc- 

 esses by a mordant, usually a salt, which enters in some manner into 

 a three-way relationship bewteen the mordant, the dye, and some part 

 of the cell. 



This chapter presents a graded series of practical exercises in 

 staining, using designated siU3Jects and a limited number of time- 

 tested stains and combinations. Staining procedures are presented in 

 the form of charts. It is easier to follow a series of operations on a 

 chart than in a written account. Staining processes fall into funda- 

 mental types, based on the character of the stains used. Each chart 

 should be regarded as a type chart rather than as a rigid set of 

 specific directions. The sequence of operations should be followed 

 closely, but the time element in some operations should be understood 

 to \ary widely. If the fitnction of each operation is thoroughly under- 

 stood, variations of the time element are easily made in accordance 

 with the reactions of the material being stained. 



Equipment 



Paraffin sections affixed to slides are stained and processed by 

 immersion in reagents in staining jars. Note the various types of jars 

 illustrated in catalogues. The most satisfactory type is the Coplin 

 jar, a \ertical jar with grooves that hold the slides in a vertical 

 position. Unlike the horizontal type, Coplin jars occupy little table 

 space, the small opening and the ground-glass lid minimize evapora- 



[55] 



