STAINS FOR UNFIXED TISSUES 489 



satisfactory manner, as it will not bear mounting in the usual media 

 without deterioration. 



Weak solutions of Bismarck broivn, quinolein-blue, anrfiii-llticJ., 

 Congo red, and neutral red (Neutral-roth) may lit- used in the same 

 way. 



Methylen-blue, used as an -infra ritnm stain, is an important 

 reagent for the study of nerve-endings. For the details of this very 

 difficult branch of technique, as well as for the methods for preserv- 

 ing the stain obtained with entire living organisms, the reader must 

 be referred to Mr. A. Bolles Lee's ' The Microtomist's Vade-mecum,' 

 in which an entire chapter is devoted to the subject. 



Stains for Fresh (Unfixed) Tissues or Organisms. The stains to 

 be mentioned under this heading resemble the i/t/i-n fitxin stains 

 described in the last paragraph in that they may be applied to living- 

 tissues or organisms. But they differ from them in that they do 

 not take effect on the objects without impairing their vitality ; on the 

 contrary they first kill them, then stain them. 



The most important of this class of stains is methyl-green. A 

 strong solution in water acidified with from ^ to 1 per cent, 

 of acetic acid is employed. The objects are soaked in the solution 

 until they are penetrated by it, then washed with pure water, or, 

 better, acidified water, and either studied therein or mounted. They 

 may be permanently preserved in any of the usual aqueous mount- 

 ing media, provided that the medium be acid or at most strictly 

 neutral, and that it contain a little of the dye in solution. Liquid 

 of Ripart and Petit, or Brim's glucose medium may be recommended 

 for mounting. It is difficult to mount the stained objects in balsam, 

 on account of the great solubility of the dye in alcohol. 



The stain is an extremely rapid one; tissues are stained almost 

 as soon as they are penetrated by it. It is, generally speaking, a 

 nuclear stain, nuclei being stained more rapidly than cytoplasm, 

 though some kinds of cytoplasm and formed material are stained by 

 it. It preserves the forms of cells well. It does not overstain, 

 and requires little washing out. This, if required, is best done wit li 

 water acidified with acetic acid. 



Bismarck brown is also a useful stain for fresh tissues. It m.iv 

 be used in solution in acidified water, as directed for methyl-gren. 

 But as the dye is not very soluble in water it is not easy to get a 

 good solution in this way, and the solutions when made keep very 

 badly. Some persons dissolve the dye in dilute glycerin (glycerin 

 diluted with one or two volumes of water). This makes a good solu- 

 tion, but on account of the shrinking action of the glycerin should 

 only be employed with objects that have been previously well fixed. 

 Bismarck brown stains quickly, and does not overstain. The stain 

 is permanent both in aqueous mounting media and in balsam. It is 

 a nuclear stain in so far as nuclei are stained by it more than proto- 

 plasm. 



The once celebrated mixture known as Ranvier's picro-carmine 

 is irrational in composition, and inconstant and frequently injurious- 

 in its effects, and is now generally abandoned. 



