216 THE AMERICAN MONTHLY [July 



the alcohol bath, carefully strip off the film, and trim it 

 round with the scalpel. The film must be removed from 

 the glass, or the air imprisoned beneath will prevent its 

 satisfactory mounting. In any case, it must be detach- 

 ed for staining. 



Staining. — The stain par excellence is Delafeld's hema- 

 toxylin, and as it is well-nigh impossible to purchase 

 this valuable reagent properly prepared, I append the 

 classical formula : — Make a saturated solution of am- 

 monia alum in distilled water, and to 100 cubic centime- 

 tres add lgr. of the finest hematoxylin crystals dissolved 

 in 5c. c. of absolute alcohol. Place this mixture in an un- 

 corked bottle and expose to daylight for a week, then add 

 25 cc. of pure glycerine and a similar quantity of methy- 

 lic alcohol. Shake thoroughly together, and expose to 

 light until the solution has deepened to an intense claret 

 color, keeping well corked ; filter ; in a month, it is ready 

 for use. It decomposes in time, but may be refiltered. 



The action is rather peculiar, insomuch as the film 

 itself does not very readily take the stain, which is more 

 than I can say for any other. Picro-carmine hopelessly 

 dyes it, the anilines do the same, and if any such are re- 

 quired to be used, the object must be treated before im- 

 bedding. Use a weak solution and stain slowly — the ac- 

 tion is far more selective, and can be checked at any stage. 

 Slightly overstain the preparations. The proper strength 

 is about five or six drops of the above solution to the 

 watch-glass of water. Wash the sections and transfer 

 to a good bulk of the stain, and turn the film occasionally. 

 Ten to twenty minutes is usually ample ; then wash in 

 water, and transfer to a saucer of weak acetic acid. This 

 decolorizes the film completely, but must not be allowed 

 to act too long, or the color of the sections will suffer. 

 The celloidin often retains a slight violet tint, in itself 

 not at all detrimental. 



Clearing and Mounting. — Unlike paraffin, celloidin 



