Staining Paraffin Sections 61 



or thinned slightly with xylene. An inexpensive and highly satis- 

 factory clearing agent, known as cnrbol-xylene, consists ot 1 volume 

 of melted c.p. phenol (carbolic acid) and 3 to 4 volumes of xylene. 



Staining Processes 



To meet the needs of teachers and beginners, staining processes 

 are arranged in a graded sequence, beginning with the simplest 

 processes, in which the variables and possibilities for errors are reduced 

 to a minimum. The simplest type of stain is a progressive stain, in 

 which the intensity of the color imparted to the tissues is proportional 

 to the length of immersion in the stain. Some of the most useful stains 

 of this type have hematoxylin as the active ingredient. In this cate- 

 gory of self-mordanting stains, the most important are Delafield's 

 hematoxylin, Harris' hematoxylin, and Mayer's hemalum. Many modi- 

 fications may be found in the literature. The term "hemalum" is 

 used in this manual to refer to any of the self-mordanting alum hema- 

 toxylins. The choice among these stains is a matter of personal 

 preference. 



HEMALUM (PROGRESSIVE) 



The modification of Mayer's hemalum, on which staining Chart 

 I is based, is selective for cellulose, pectin, fungus mycelium in many 

 cases, weakly selective for chloroplasts, strongly selective for metabolic 

 (resting) nuclei, and moderately selective for chromosomes in some 

 subjects. Hemalum may be used without any other stain for meriste- 

 matic organs, for anther and ovary slides in which a critical chromo- 

 some stain is not necessary, and for subjects having but little strongly 

 lignified or differentiated tissues. This stain develops a metallic 

 scum on standing. The particles of this scum adhere to the adhesive 

 and to the sections on the slide, therefore the stain should be filtered 

 before using. 



The preliminary processing of slides, prior to immersion in stain, 

 is essentially the same regardless of the stain used. This prestaining 

 process will now be outlined and the procedure is understood to 

 apply when an aqueous stain is used. After the affixed sections have 

 been dried in the 53°C. oven, the sections and adjacent parts of the 

 slide are found to be coated with melted paraffin from the ribbon. 

 Obviously, the first operation is to dissolve this paraffin by immersing 

 the slide in a jar of xylene. If slides are taken directly from the oven, 



