APPENDIX A 257 



water to the colour of brown sherry. The reagent may also be 

 prepared by diluting the liquor zW/of the Pharmacopoeia. This 

 is the ordinary iodine solution in common use in the laboratory. 



ii. The alcoholic solution may be prepared by dissolving 

 crystals of iodine in alcohol, and diluting with alcohol to a dark 

 sherry colour ; also by diluting the tinctura iodi of the Pharma- 

 copoeia : in the absence of water this solution does not give the 

 blue reaction with starch. 



iii. A solution of potassium iodide and iodine in pure glycerine 

 is sometimes used in the treatment of crystalloids. 



iv. The solution of iodine in chloral hydrate is used for 

 detection of included starch-grains (see above, Chloral 

 Hydrate). 



v. For the solution in chloride of zinc (Schulze's solution), see 

 above, Chlor-Zinc-Iodine. 



The ordinary solution of iodine (i) stains proteid substances, 

 and especially the nucleus, brown ; cellulose faintly yellow ; 

 cuticularized and lignified walls yellow ; gum purple and starch 

 blue. Together with sulphuric acid, iodine colours cellulose 

 blue, a reaction similar to that with chlor-zinc-iodine. 



Methyiene Blue is used in solution in water : it stains the cell- 

 wall, but not the protoplasm. 



Methyl-green. A tolerably strong alcoholic solution of this 

 is used. The sections of the object, which must have been 

 previously kept in absolute alcohol, are to be treated with the 

 staining-fluid for from 5-25 minutes, then quickly washed with 

 distilled water, and mounted in glycerine. The nucleus stains 

 of a green or bluish-green colour, the protoplasm remaining 

 uncoloured. It is especially good for staining nuclei which are 

 dividing, and for bringing out the nuclei in the cells of Fungi 

 and of the Siphoneae, for which purpose Strasburger recommends 

 the following method : The fresh object or section is mounted 

 in 2 per cent, acetic acid, to which a little methyl-green has 

 been previously added : the nuclei are fixed almost instantane- 

 ously and at the same time stained. These preparations may 

 then be washed in I per cent, acetic acid, and be mounted in 

 weak glycerine and acetic acid. Objects stained with methyl- 

 green fade very rapidly. 



S 



