12 W. H. E M I G 



destaining of basic dyes with acid-alcohol has been omitted from 

 the technique described in this text. 



Physical properties. In a few staining procedures the ab- 

 sorption of color is entirely physical. If sections of germinating 

 corn grains remain in a solution of Sudan IV, the tissue containing 

 fats stains a bright red. The dye is absorbed by the fats but not 

 by the proteins or carbohydrates. Here, the oil soluble dye, un- 

 changed chemically, is held in suspension. The dye is extracted 

 from the fatty tissue as soon as the stained sections are changed to 

 strong alcohol, acetone, or xylene. In a similar manner, a dye dis- 

 solved in an oil such as clove oil or aniline oil is retained by a tissue 

 in the same form as it occurs in the oil suspension. Colors pro- 

 duced in this manner are not oxidized pigments; they disappear 

 gradually or dissolve in balsam. 



