STAINS AND STAINING 43 



spectrophotometric tests, has been tested chemically, and has been 

 tried in actual practice. The advantage to the one who uses stains is 

 that, when he finds a certified stain which is satisfactory, he can al- 

 ways get exactly the same stain again. 



The earlier stains, even the Griibler stains, were merely textile 

 dyes, usually more or less modified. A student once asked Professor 

 W. J. G. Land what was the difference between gentian violet and 

 crystal violet, and received the reply, "Gentian violet is crystal 

 violet plus mud." Textile dyes were often weakened or adulterated. 

 Biological Stains, an excellent book by Dr. Conn, gives not only an 

 account of the work of the commission but also an interesting history 

 of stains and staining. 



Stains may be classified in various ways: e.g., there are three great 

 groups of stains — the carmines, the haematoxylins, and the anilins. 

 Stains may be classified as basic and acid, or they may be regarded as 

 general and specific. A general stain affects all the elements, while a 

 specific stain affects only certain elements, or stains some elements 

 more deeply than others. Stains which show a vigorous affinity for the 

 nucleus have been called "nuclear stains," and those which affect the 

 cytoplasm more than the nucleus have been termed "plasma stains." 



Of course, such stains are specific. 



We shall consider some of the more important haematoxylins, car- 

 mines, and anilins, reserving general directions and theoretical ques- 

 tions for another chapter. The formulas are largely empirical. Some 

 of those given here are taken from The Microtomist's Vade-Mecum 

 (Lee), which is easily the most complete compendium of stains and 

 other reagents concerned in microtechnique. Biological Stains, al- 

 though not covering so much ground, is, in many respects, superior, 

 and the formulas are for the standardized stains. 



Other formulas are from Botanical Microtechnique (Zimmermann) 

 and from Stirling's Histology, and still others are from current litera- 

 ture and from our own laboratory. The directions for using a stain 

 apply to stains made up according to the formulas which are given 

 here, and may need modification if other formulas are employed. It is 

 hoped, however, that the directions will give the student sufficient 

 insight into the rationale of staining to enable him to make any neces- 

 sary modifications. Since American stains have come into general 

 use, the need for rationale is even greater, especially if the American 

 stains are made up according to standard formulas, which are based 



