CHAPTER XV. 



PLASMA STAINS* WITH COAL-TAR DYES. 



290. Introduction. --By a plasma stain is meant one that 

 stains the extra-nuclear parts of cells and the formed material 

 of tissues, or one of these. 



The plasma stains described in this chapter are for the 

 most part those obtained by means of "acid' dyes ( 203); 

 but some of them are obtained by means of "neutral' dyes 

 ( 203), and a few by "basic' dyes. 



The mode of staining is generally progressive, almost 

 always so when acid colours, used substantively ( 205), are 

 employed. But the regressive method, with differentiation, 

 is sometimes made use of, especially when a mordant has 

 been used with the dye. 



In some processes, e. a., Flemming's orange method, a 

 basic and an acid dye (or vice versa) being employed in suc- 

 cession, there is formed in tJic tissues a neutral colour ( 203) 

 which effects .the desired stain. These maybe considered as 



/ 



adjective stains, the first colour serving as a mordant for 

 the second. Not any two dyes taken at haphazard will 

 behave in this way : they must be such as to form by com- 

 bination a suitable neutral lake (cf. 203). The basic dye 

 may be made the primary stain, as in Flemming's process : 

 or the contrary. 



In such stains as Beinke's orange method, or the Ehrlich- 

 Biondi mixture, and many others, one or more neutral colours 

 are formed in tJ:e mixture and stain progressively. 



I am not acquainted with any plasma stain that is 



* This chapter includes only such stains as are used in. ordinary work 

 on tissues in hulk or sections, stains for fpecicd purposes being treated 

 under " Nervous tissue," " Blood," etc. It includes some double or 

 triple stains that affect nuclei as well as plasma, but in different- hues. 



