STAINING REAGENTS. 63 



XII. STAINING REAGENTS. 



Staining. This process depends on the fact that different tissues, 

 or different parts of the same tissue, have an affinity for certain dyes, 

 and not for others. Thus some dyes stain only the nuclei, others 

 however may cause a uniform stain, all the tissues being of the same 

 colour. By using some decolorising reagent, it is possible to remove 

 the stain from certain parts of the preparation, leaving other parts 

 stained. 



A thin section of a tissue or an organ, as a rule, when examined 

 shows but little differentiation of its several parts. Only in cases 

 where pigment is naturally present is this difference very marked. 

 Some substances when applied to the section stain one part and 

 leave other parts unaffected, thus enabling one to differentiate more 

 easily the several parts of a section. 



Those substances which stain the nuclei chiefly have been called 

 nuclear stains. The section is placed in a weak solution of the dye, 

 e.y., haematoxylin ; and after it seems to be sufficiently stained, the 

 surplus dye is removed by thoroughly washing the section in water 

 or alcohol, a part of the dye remaining united with the chromatin of 

 the nucleus and colouring the latter. Such stains may also colour 

 to a less degree some other parts of the section. Amongst nuclear 

 stains are carmine, hsematoxylin, and some of the aniline colours. 



"When a section is stained, it is called Section Staining, but the 

 tissue may be stained in bulk before the sections arc made (p. 44) 

 staining in bulk. 



A. Carmine and its Compounds. 



Carmine. In order to obtain a strong solution of this dye, 

 certain solvents require to be employed. It is readily soluble in 

 ammonia, yielding an ammoniacal solution, which may be made 

 strong or weak. The ammoniacal solution may be diluted to any 

 extent required with water, and practically the best results are 

 obtained by allowing sections to remain for a long time (24-48 

 hours) in a weak solution. 



1. Strong Ammoniacal Carmine Solution. Eub up in a mortar 

 2 grams of pure carmine with a few drops of water, add 5 cc. of 

 strong liquor ammonise, mix thoroughly, and add 100 cc. of water. 

 Place the whole in a bottle, and after a day or so any undissolvcd 

 carmine is filtered off and the clear fluid kept as a stock solution. 

 This solution may he diluted to any required extent. If it smell 

 Strongly of ammonia, the excess of ammonia must be allowed to 

 evaporate. When the solution becomes neutral it is very liable 

 to undergo putrefaction, but this may be avoided by placing a 

 small piece of thymol in it to preserve it. 



