548 POWDERED DRUGS 



.a solution of potassium iodide and iodine. It is said to act more quickly than 

 chloroiodide of zinc and iodine and the color imparted is retained for several days. 



Iodine and Glycerine. A mixture of potassium iodide-iodine with glycerine 

 in equal parts gives good results when the action of iodine is to be observed. The 

 glycerine keeps the preparation from drying, and at the same time has a clearing 

 effect. 



Iodine and Potassium Iodide. This solution is prepared by dissolving 0.5 

 Gm. of potassium iodide and I Gm. of iodine in a small amount of water, and then 

 diluting this with 100 mils of water. The solution is left standing over any iodine 

 which may crystallize out. This formula is commended by Arthur Meyer in his 

 work on " Starkekorner" as best adapted to the study of starch-grains. A rough- 

 and-ready method of preparing an iodine solution is to dissolve a small amount of 

 potassium iodide in distilled water and then dissolve crystals of iodine in this until 

 a brown color is obtained. This can be diluted with water as is found necessary. 

 A rather pale solution of iodine is sufficient to color starch blue. To stain modified 

 cell-walls the solution needs to be stronger. 



Iodine and Sulphuric Acid. A test for cellulose. The section is first soaked 

 in a solution of potassium iodide-iodine, and then is mounted in a drop of a mixture 

 of 2 parts by volume of sulphuric acid and i part of water. Cellulose walls take on 

 a blue color by this process. 



Iodine Green. See under Double Staining. A 2 per cent, solution of glacial 

 acetic acid with iodine green dissolved in it serves well in the instant fixing and 

 staining of the nuclei of fresh material. 



Iodine water is prepared by adding as much iodine to distilled and sterilized 

 water as it will dissolve (about I : 5,000). 



Iron Acetate. Used in the detection of tannins, which see. 



Iron Haematoxylin. See Double Staining. 



Lactic Acid. Dried alga? and fungi may be prepared for study with the micro- 

 scope by soaking them first in water and then in concentrated lactic acid, in which 

 they are heated until small bubbles are formed; they may then be studied in the 

 lactic acid. A 10 per cent, solution of lactic acid is recommended for fixing bacteria. 

 This fixative is said not to interfere in any way with the subsequent processes of 

 staining with alcoholic solutions of aniline dyes. 



Lead Acetate. A 10 per cent, solution of neutral lead acetate is used to harden 

 the mucilaginous layers of seed coats. For subsequent treatment see under Boracic 

 Acid. 



Lithium Carbonate. Useful in removing from material picric acid, which has 

 been used as a fixative. A few drops of a cold, saturated, aqueous solution of 

 lithium carbonate are added to the alcohol, which is used to wash out the fixative. 



Loeffler's Methylene Blue. This reagent is prepared by adding 30 mils of a 

 concentrated alcoholic solution of methylene blue to 100 mils of water containing 

 10 milligrams of potassium hydrate. 



Maceration. The study of the forms of cells is greatly aided by isolating the 

 cells from each other by the process known as maceration. Various reagents may 

 be used for this purpose. A solution of potassium chlorate in nitric acid is very 

 commonly employed. This is known as Schulze's maceration fluid. A few pieces of 

 potassium chlorate are put into a test-tube, where they are covered with nitric acid ; 

 not very thin longitudinal sections of the material to be macerated are put into the 

 solution, which is then gently heated over a Bunsen burner until bubbles are vio- 

 lently evolved. After standing for a short time the contents of the tube are poured 

 into a vessel containing considerable water. The sections should be transferred 



