DS 00-DS 10 



DYE STAINS OF GENERAL APPLICATION 



271 



colored lake ("calcium alizarinate") is 

 formed between the bone and dye, result- 

 ing in a (juite sharp differential staining 

 after tlie extraction of the excess dye with 

 alkalis in which the lake is insoluble. 



It is difficult to maintain today the old 

 distinction between direct and indirect 

 staining. In the former instance the stain 

 was applied from a very weak solution on 

 the assumption that it would be differ- 

 entially absorbed by varjdng structures 

 and tissues. Actually, however, in the 

 majority of these methods, the density of 

 the tissue controls the degree of absorp- 

 tion. Indirect methods are those in which 

 the dye is appHed from a relatively strong 

 solution and is subsequently dissolved 

 away, or extracted, from the unwanted 

 structures either by a solvent or b}' some 

 additional chemical reagent. 



The last method of staining which is 

 commonly employed is that of mordant 

 staining, in which the tissue is first caused 

 differentially to absorb a substance with 

 wliich the d3'e subsequently makes an in- 

 soluble compound. Nuclear stains are the 

 most widely used by this method, al- 

 though it is probable that in many in- 

 stances the metals employed in fixative 

 solutions do themselves act as mordants. 

 In the majority of cases tissues fixed by 

 methods other than those specified for a 

 particular staining technique may be 

 rendered available for this technique if 

 the sections attached to the slide are mor- 

 danted in the required fixative before 

 staining. 



DS 02 METHOD OF ARRANGE- 

 MENT OF FORMULAS 



The original method of classification for 

 stains was to divide them into basic {i.e., 

 nuclear staining), acid (i.e., plasma stain- 



DS 10 Dye Staining Techniq 



It cannot be too strongly emphasized 

 that the selection of a dye staining tech- 

 nique for the general purposes of histology, 

 embryology, and cytology is a matter in 

 which the investigator should use his own 

 initiative rather than rely on his knowl- 

 edge of what has been done before. In too 

 many cases a relatively worthless tech- 



ing), and neutral groups. This method has 

 been rendered obsolete by the employ- 

 ment of d\-es in formulas which alter their 

 basic staining reactions. The method of 

 classification adopted by Langeron in the 

 numerous editions of his Precis de Micro- 

 scopic is based upon the chemical nature 

 of the dyes themselves, and would appear 

 at first sight to be the most logical. This is 

 not, however, as good in practice as in 

 theor}', for it results in the widespread 

 separation of formulas which, in lab- 

 oratory practice, are, or should be, 

 interchangeable. 



Tlie classification given at the begin- 

 ning of this chapter has been erected on 

 the principal that those solutions which 

 may be profitably interchanged for each 

 other upon the laboratory bench should 

 have their formulas published under the 

 same heading. The first step has, there- 

 fore, been the removal of "Techniques of 

 Special AppUcation" to Chapter 21. This 

 chapter does not contain all those stains 

 which have been proposed for special pur- 

 poses, but only those which experience has 

 shown to be otherwise valueless. The triple 

 stain of Kull 1913, for example, which is 

 widely employed for the demonstration of 

 mitrochondria, has many other uses, and 

 is accordingly placed with Rhamy 1930, 

 which it resembles. Both are, however, 

 mentioned as cross references in the divi- 

 sion of the special section for which they 

 were proposed. 



Each of these two chapters has been 

 further divided into convenient subdiAd- 

 sions, which in some cases are founded 

 upon the components of the solutions, in 

 other cases upon their practical use. The 

 result is that every formula is accom- 

 panied either by those formulas or by 

 references to those formulas, which may 

 be employed as a substitute. 



ues of General Application 



nique has been applied j^ear after year for 

 no other reason than that it has become 

 conventional to do so. Were this reasoning 

 to be taken to its logical conclusion and 

 techniques utilized only for the original 

 purpose for which they had been invented, 

 we sliould find tliat the use of Bouin's 

 picro-formaldehytle-acetic fixative would 



