558 POWDERED DRUGS 



weight of distilled water. With tincture of iodine added this reagent will cause 

 starch to swell, at the same time imparting a blue color to it. 



Salt. A 4 per cent, or stronger solution of common salt, or of potassium nitrate, 

 may be used to cause plasmolysis in living cells. This process may be all the more 

 clearly seen by adding eosin to the salt solution. 



Schulze's macerating solution is prepared by adding crystals of potassium 

 chlorate from time to time to warm concentrated nitric acid. It is employed 

 in the isolation of lignified cells. The material is allowed to remain in the solution 

 for a short time or until there appears to be a disintegration of the tissues. A large 

 excess of water is then added. The material is carefully washed, the cells teased 

 apart and mounted in a solution of methylene-blue. 



Shellac. A thick solution of shellac in alcohol, to each ounce of which are added 

 20 drops of castor oil, makes an excellent sealing medium for preparations mounted 

 in glycerine or glycerine-jelly, or in an aqueous medium. 



Silver Nitrate. A solution of silver nitrate is used to bring out more clearly 

 the striations in bast fibers and starch-grains. Sections containing striated bast 

 fibers are allowed to dry and are then impregnated with the silver salt. Without 

 previous washing the sections are transferred to a 0.75 per cent, solution of common 

 salt. They are then placed in distilled water and exposed to the light for a consid- 

 erable time; thereafter they are allowed to dry and may be examined to good ad- 

 vantage in anise oil. 



Dry starch-grains are put to soak in a 5 per cent, solution of silver nitrate. 

 After a time they are allowed to dry superficially and are then treated with a 0.75 

 per cent, solution of common salt, in which they are finally exposed to the direct 

 light of the sun to reduce the chloride of silver which has been formed within the 

 grains. The less dense laminae of the starch-grains will show a gray color, due 

 to the reduced silver. 



Staining Intra Vitam. Living protoplasts may accumulate certain stains from 

 very dilute solutions without injury to themselves. Dahlia, methyl- violet, mauvein, 

 and methylene-blue are particularly suitable for this purpose. Solutions contain- 

 ing o.ooi per cent, or 0.002 per cent, of any of the first three stains have given good 

 results in staining living nuclei, while i part of methylene-blue in 500,000 parts of 

 filtered rain-water is used for staining living cells containing tannin. A large amount 

 of these very dilute solutions should be employed in order that a sufficient amount 

 of coloring matter may be at hand for accumulation by the living cells. Living 

 protoplasts have the power of reducing and accumulating metallic silver from solu- 

 tions of certain of the salts of silver, while dead protoplasts have not this power. 

 The simplest method of producing this reaction is to place a few filaments of 

 spirogyra in a liter of a mixture of i part of silver nitrate in 100,000 parts of water 

 with 5 mils of lime water. The experiment will be completed in about half an 

 hour if the temperature of the solution is raised about 3OC. By this process 

 living protoplasts are colored black by the reduced silver, while dead protoplasts 

 take on a yellowish or brownish color. 



Sulphuric Acid. By the action of sulphuric acid cellulose is changed to amyloid, 

 which may be colored blue by a tincture of iodine. By the continued action of con- 

 centrated sulphuric acid cellulose becomes dissolved. Cutinized and lignified 

 membranes remain undissolved in sulphuric acid. Silicious skeletons or incrusta- 

 tions may be freed of all organic matter by treating the objects with concentrated 

 sulphuric acid until they turn black, and then with a 20 per cent, aqueous solution 

 of chromic acid. The objects should be washed repeatedly in water before they 

 are ready for examination with the microscope. 



Tannin and Antimonium-potassium Tartrate. These are used successfully as 

 a mordant for methyl- and gentian-violet, fuchsin, and safranin when sections 



