5°- ELEMENTS OF APPLIED MICROSCOPY. - 



and thus emphasize their outhne and bring out the struc- 

 ture more clearly. Sometimes the stain acts upon a 

 certain tissue as a whole, picking it out from other tissues; 

 surrounding it. More generally, however, the substances; 

 used act on a certain part of the individual cell, generally, 

 the nuclteus, making that structure stand out clearly; 

 from the cytoplasm. 



Staining processes are often complicated, and include, 

 not only direct methods in which the stain is allowed to 

 act just long enough to affect the desired elements and; 

 then washed out, but also indirect methods in which the 

 tissue is overstained and the dye then removed by alco- 

 hol or acid from the parts which give it up most readily.- 

 Small objects may be. stained in bulk and , section^ 

 treated on the slide. 



Of the staining solutions used, hamatein and the 

 anilin dyes (fuchsin, methylene blue, eosin, safranin, 

 Bismarck brown, etc.) are the most generally useful. 

 By a proper combination of two of these it is possible to 

 stain the cytoplasm of the cell one color and the nuclei 

 another. This process of double staining depends of 

 course on the greater avidity of the nuclear substance 

 for most dyes. A good example for practice in double 

 staining is the hsematein- eosin combination. The secy 

 tion, attached to the slide with albumin fixative, and 

 cleared, is passed down through the grades of alcohol to 

 30%, and is then placed for one or two minutes in a solu- 

 tion of Mayer's haemalum.* The section is then washed 



*Mix I gram haematein dissolved in 50 cc. of 90% alcohol, With 

 50 grams alum dissolved in 1000 cc. water. Cool, settle, and filter 



