DOUBLE STAINING. 



It is often desirable, in order, to bring out more clearly some 

 part of a specimen, to stain different portions of it with separate 

 colors. This is very easy to bring about if the proper stains are 

 employed. For example, the xylem of a fibro-vascular bundle can 

 be stained one color and the phloem another. These results are 

 very important in research as one is enabled to recognize in this 

 way similar tissues in different parts of a specimen where other- 

 wise they might be somewhat difficult to distinguish. Certain 

 stains will color one part of a tissue or special part of a cell, and 

 yet not effect in any way other portions. 



The combinations of stains that can be used for this purpose 

 are very varied, and the results in the case of some quite uncertain 

 to predict, consequently no general rule can be laid down in regard 

 to the kind of tissue any stain will invariably act upon. 



With regard to the treatment, in general the selective stain 

 should be applied first, and in dilute solutions. The sections 

 should then be thoroughly washed and the general stain applied, 

 the tissue washed again and mounted directly in glycerin jelly or 

 dehydrated, cleared, and mounted in balsam. Glycerin jelly is per- 

 haps a better mounting medium for double stained tissue, since the 

 alcohol and clearer are often injurious in their bleaching effect. 

 Some combinations of stains whose effects can be depended upon 

 are haematoxylin and eosin or picro-carmine, iodine green and eosin, 

 carmine or haematoxylin with picric acid, and methyl green and 

 eosin. 



It is often necessary to use a mordant to fix the stain, in which 

 case a saturated solution of alum can be applied to advantage. A 

 little experience with double staining will enable one to . use it in a 

 way that will be of great assistance to a better interpretation of 

 the character of many tissues. 



