COLORING AGENTS. 51 



If the preparation should be too deeply stained 

 by this carmine fluid, it can be bleached in an 

 alcoholic solution of oxalic acid. 



Carmine stains all protoplasm if allowed to act 

 a sufficient length of time. The nuclei of cells are 

 most deeply colored. Living protoplasm does not 

 imbibe the coloring matter. This occurs only 

 after it has been killed by the addition of the 

 reagent. In general it may be said that it colors 

 most vegetable albuminoids, while starch and 

 cellulose take it up in much smaller quantity or 

 not at all. 



[The double-staining of clear sections, usually 

 bleached by the action of Labarraque's solution, or 

 some similar fluid, is capable of yielding very 

 good results where convenience of demonstration 

 in the class-room is concerned. As good direc- 

 tions as any are those of Dr. Rothrock, 1 who uses 

 Woodward's ammonia carmine and the aniline 

 color known as iodine-green. 



The section is placed in alcohol faintly colored 

 by the addition of a few drops of a concentrated 

 tincture of the green, where it is allowed to remain 

 from twelve to twenty-four hours, according to 

 circumstances. It is then successively passed 

 through a series of fluids in the following order : 

 one, water ; two, carmine ; three to five, alcohol ; six, 

 absolute alcohol ; seven, oil of cloves : being merely 



1 Rothrock : Staining and double-staining of vegetable tissues. Bot. 

 Gazette, Sept. 1879, Vol. IV., pp. 201-6. 



