APPENDIX. 397 



F The uses of ordinary iodine solution (either the diluted tincture 

 or the potassium iodide solution) are various. It stains starch blue, 

 proteins brown, cellulose walls pale yellow, lignified and cutinised 

 walls deeper yellow, and gums violet. Together with sulphuric 

 acid, iodine makes cellulose walls blue or violet. See also Chloral 

 Hydrate and Clilor zinc-iodine. 



Iodine Green is a useful general stain. (1) For instant fixation 

 and staining of the nuclei of fresli material, use iodine green dis- 

 solved in 2 per cent, acetic acid. (2) Iodine green stains lignified 

 walls, and can be used in conjunction with erythrosin or fuchsin in 

 double staining. 



Iron Acetate is used as a test for tannin. The sections are 

 placed in alcohol to remove the chlorophyll, if present, then in iron 

 acetate solution ; a blue or green colour is produced by tannin. 



Iron Chloride or Iron Sulphate, in aqueous solutions, are 

 also used as tests for tannin, the colour produced varying from blue 

 to green. 



Lead Acetate. -Make a saturated aqueous solution. To make 

 lead acetate papers, dip strips of filter paper into the solution ; on 

 exposure to the action of sulphuretted hydrogen, the paper will turn 

 black owing to formation of lead sulphide. To detect presence of 

 sulphur in organic substances, heat with soda lime, and hold a lead 

 acetate paper over mouth of tube. 



Maceration. Various reagents are used to isolate the cells of a 

 tissue. (1) Schultze's process is perhaps the best where ligniHed 

 tissues are present. Place a little strong nitric acid in a test-tube, 

 add a crystal of potassium chlorate, heat to boiling, and drop in the 

 sections ; when these turn white, pour the contents of the tube into 

 a dish of water, and tease out the material on a slide. (2) Mangin's 

 process : place the sections for a day or two in a mixture of 3 

 volumes alcohol and 1 volume of hydrochloric acid, rinse them in 

 water, place in 10 per cent, ammonia for 15 minutes, then mount 

 the section in water and press on the cover-glass to force the cells 

 apart. (3) Chromic acid is also used for maceration. Place the 

 sections in concentrated aqueous solution for a minute or two, rinse 

 in water, mount in water and press on the cover ; if the cells do not 

 come apart, put the specimen for a longer time in the acid. 



Methyl Blue, used in aqueous solution, is a good stain for cellu- 

 lose walls, especially when used with safranin as a double stain. 

 Stain with the safranin overnight, rinse in water, and then in acid 

 alcohol, place in strong methyl blue solution for 15 minutes, treat 

 with strong alcohol and pass through clove oil or xylol into balsam. 



Methylene Blue. (1) A good stain for the nucleus, especially 

 for cells filled with protein grains. (2) Cells containing tannin 

 accumulate methylene blue from very dilute solutions, e.g. 1 part of 



