Ill 



STAINING. 



71. While staining has a value in histology in coloring the 

 preparation as a whole and thus making its parts stand out more 

 sharply, the aim is to employ such stains as by their selectivity give 

 different parts or structures different colors or intensities of color, 

 thus differentiating them the better. 



In histology, selective stains are employed (a) to color the 

 nucleus differentially, thus distinguishing it sharply from the cell 

 body, and by means of the nucleus setting apart groups of cells ; 

 (b) to distinguish between different kinds of tissue, as, for example, 

 connective tissue and muscle. 



72. The following two general rules may be given : 



1 i ) The preparation should be transferred to the stain from 

 the fluid in which the staining principle is dissolved. The majority 

 of the stains employed are aqueous solutions ; some, however, such 

 as hydrochloric acid carmine, are alcoholic ; with these alcoholic 

 stains the last preparatory step ( 70), removal of the alcohol by 

 water, should be omitted. Many stains may be used either in 

 aqueous or in alcoholic solution. 



(2) The stain should be washed out with the solvent of the 

 dye, water or alcohol as the case may be. 



With many aniline dyes ( 74) one may, and in many cases 

 should, employ alcohol for washing out, even though the staining 

 solution is aqueous. 



73. Differentiation. To bring out the differential or 

 selective coloring of the dye. This is necessary with many stains, 

 especially anilines, and may often be satisfactorily accomplished by 

 the use of 95% alcohol and made a part of the washing out. Alcohol 

 acidified with hydrochloric acid ( 149) is sometimes used, or a 

 special differentiator is required. 



74. Classification. (#) According to their chemical nature 

 the stains generally used are (i) hematoxylin stains, (2) carmine 

 stains, (3) aniline stains 



(d) According to their selectivity. Stains as used in histology 

 may for convenience be classified as (i) nuclear, (2) general, and 

 (3) special. These are often used in combinations of two or three, 

 either together in the same solution or separately in solutions used 



