494 PREPARATION, MOUNTING, AND COLLECTION OF OBJECTS 



may clear or remove the alcohol with an agent that does not remove 

 any more colour, such as cedar oil, or bergamot oil, or xylol, toluol, 

 or benzol. This being done, nothing more remains but to add a drop 

 of xylol-balsam or dammar, and a cover (chloroform is best avoided, 

 either as a clearer or as a menstruum for the mounting medium). 



The result is a pure nuclear stain, of exceeding brilliancy, and 

 perfectly permanent in balsam. 



The process is not available for staining in bulk, but besides 

 sections such material as is thin enough to behave like a section 

 portions of thin membranes, for instance may be stained in this way. 

 The process of differentiation takes about a couple of minutes with 

 most thin sections, but in some cases considerably more is required. 



Besides safranin, many others of the coal-tar dyes may be used 

 in the same way : for instance, basic fuchsin (magenta), also a red 

 stain, or gentian violet or thionin, both these being blue. Thionin is 

 peculiarly resistent to alcohol, which is an important quality in some 

 cases. 



Plasma Stains, or Plasmatic Stains, All the stains we have 

 hitherto considered (with the exception of the infra vitam stains) 

 have been nuclear stains that is, such as- stain nuclei either 

 exclusively, or at least more energetically than protoplasm or formed 

 material. In very many cases they perform all that the histologist 

 requires in the way of rendering structure visible. But still there 

 are other cases in which it is desirable to obtain a separate stain of 

 extra-nuclear parts. For this purpose the so-called plasma stains 

 are employed. 



Picric acid is a useful one, especially when employed after a 

 carmine or hsematoxylin nuclear stain. The modus operandi is as 

 simple as possible : it consists merely in adding picric acid to the 

 alcohol employed for dehydrating the objects, and leaving them 

 therein until the desired intensity of stain is obtained. ' It has the 

 great quality, shared by very few plasma stains, that it can be used 

 for staining entire objects. And as it is extremely penetrating, it is 

 very much indicated for the preparation of such objects as small 

 arthropods or nematodes, mounted whole.' 



Lyons blue (Bleu de Lyori) is a good plasma stain that will work 

 well after carmine- (borax-carmine for instance). It may be used 

 for staining in bulk, in a very dilute alcoholic solution ; or for 

 staining sections, in a strong aqueous solution. The objects must 

 not remain too long in alcohol after staining. 



The dye known as Wasserblau (water -blue] gives with sections 

 a similar but perhaps more delicate stain. It is a good stain to 

 use in conjunction with safranin, using the Wasserblau first. The 

 process is, first, to stain rather strongly in a concentrated aqueous 

 solution of the blue, and then for from half an hour to four or five 

 hours in the safranin, as described above. 



Either of these stains will probably be found safer than indigo- 

 carmine, which w r as once much employed for similar purposes. 



A still more precise and delicate plasma stain is /Sdurefuchsin 

 (also known under the synonyms, or names of brands, of acid 

 fuchsin, Xaurerubin, Fuchsin S, Rubin 8, and others). It is 



