CHAPTER XVI. 



THE COAL-TAR PLASMA STAINS. 



280. As to Plasma Stains. By a plasma stain is generally 

 meant, rather vaguely, one that stains the extra-nuclear parts 

 of cells and the formed material of tissues, or one of these. 

 To be precise the class ought to be subdivided, and we 

 ought to speak of cytoplasm stains, granule stains, ground- 

 substance stains, or the like. But the vague general sense 

 of the term will be sufficient for the purposes of the present 

 chapter. 



Good plasma stains are much wanted. Unfortunately- 

 such a thing can hardly be said to exist ; for it is not enough 

 to require of a plasma stain that it should stain extra-nuclear 

 material. It is also desirable that it should do so in as 

 selective a way as possible. Now all plasma stains are 

 more or less diffuse stains. Many exhibit considerable 

 selectivity, but it is by no means always easy to get them 

 to display the particular selectivity that is desired. Those 

 that do not display it are of little use, or of none at all. I 

 have therefore suppressed a large number of formula; which 

 appear to me to have little or no scientific value. Most of 

 them, if required, will be found quoted in the previous 

 editions. 



281. Picric Acid. I follow FLEMMING (Zeit. f. wiss. Mile., i, 

 1884, p. 360) in pointing out that picric acid is one of the 

 most generally useful of all secondary stains. It gives useful 

 plasma stains with most of the nuclear stains, and particularly 

 with carmine and ha3matoxylin. The modus operandi is as 

 simple as possible: it consists merely in adding picric acid 

 to the alcohols employed for dehydrating the objects after 

 staining with a nuclear stain. 



