APPENDIX. MOUNTING OR ENCLOSING MEDIA. 215 



until the gelatine is completely dissolved ; add four ounces of pure glycerin 

 and as many drops of 95 per cent, carbolic acid, gently stirring the mixture 

 with a glass rod, so as to mix thoroughly, but not to form air bubbles, and then 

 allow the mixture to cool. It will soon set and form a clear, transparent jelly. 

 If the gelatine used be of the finest quality, and perfectly free from dust, which 

 may be insured by rinsing rapidly in cold distilled water before using, no filter- 

 ing or straining will be necessary. It should be kept in a test-tube, so that 

 when required for use it may readily be melted. 



Many structures are rather better defined when mounted in glycerin jelly 

 than when mounted in balsam, aDd it is also less troublesome to use, as com- 

 plete anhydration is not necessary. Delicate structures must not, however, be 

 transferred immediately to the glycerin jelly, for this would cause the cells to 

 collapse by osmosis, but they are first removed to very dilute glycerin and then 

 successively to solutions of gradually increasing strength, until strong glycerin 

 is reached, after which they may safely be enclosed in the medium. A more 

 convenient method is to place the object in very dilute glycerin and permit this 

 to gradually concentrate by the evaporation of its water. Still another way, 

 and a good one, is to place some strong glycerin in a test-tube, say enough to 

 fill it half full, then pour on its surface enough water to make a thin layer over 

 it, taking care to mix the liquids as little as possible. The object is then care- 

 fully placed in the water and the tube allowed to remain undisturbed for a few 

 days. It will then be found that the object has settled into the strong glycerin 

 so gradually, that no damage has resulted to it from osmosis. This method is 

 a very convenient and successful one for filamentous algas. 



Carmine stained preparations are unsuited to this medium as the carmine 

 is soluble in it. The same is true of some of the anilin preparations. Hxma- 

 toxylin-stained specimens keep well in the medium, providing it contains no 

 trace of acid. 



Hoyer's Fluid for Anilin Preparations. This is made as follows : A tall 

 wide-mouthed vessel is filled two-thirds full with the best selected gum Arabic. 

 The vessel is then filled to the neck with a 50 per cent, solution of potassium 

 acetate in distilled water, and the mixture is permitted to stand for a few days, 

 occasionally agitating it, until complete solution has taken place. A tuft of 

 glass wool is then moistened in distilled water and packed, not too tightly, in 

 the apex of a funnel, and the thick liquid permitted to filter through it. 



This is a good enclosing medium for any of the preparations stained with 

 the anilin dyes, but is not suitable for carmine or haematoxylin preparations. 

 For these, the following is used : 



Hoyer's Fluid for Haematoxylin and Carmine Preparations. This is the 

 same as the other, except that the solvent used is a concentrated solution of 

 chloral hydrate in distilled water, to which 5 or 10 per cent, of pure glycerin 

 has been added. 



Specimens should not be transferred to either of these fluids direct from 

 water but from strong glycerin. Preparations mounted in them are permanent, 

 but greater safety to the mount is insured by running a ring of balsam of Fir 

 or of asphaltum around the edge of the cover-glass. 





