328 REAGENTS AND PROCESSES 



grains will show a gray color, due to the reduced silver. See 

 page 177 for a description of the structure of starch grains. 



Staining Intra Vitam. Living protoplasts may accumu- 

 late certain stains from very dilute solutions without injury to 

 themselves. Dahlia, methyl-violet, mauvein, and methylene- 

 blue are particularly suitable for this purpose. Solutions con- 

 taining 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 accumula- 

 tion by the living cells. Living protoplasts have the power of 

 reducing and accumulating metallic silver from solutions 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 c.c. of 

 lime-water. The experiment will be completed in about half an 

 hour if the temperature is approximately 30 C. 



Tannin and Antimonium-potassium Tartrate. These 

 are used successively as a mordant for methyl- and gentian- 

 violet, fuchsin, and safranin when sections stained with these 

 are to be mounted in glycerine. The sections before staining 

 are placed in a 20 per cent, solution of powdered tannin in cold 

 water. After washing well in distilled water, they are placed 

 for twenty-four hours in a 2 per cent, solution of antimonium- 

 potassium tartrate. After washing again in distilled water, 

 they are transferred to the stain. From the stain the sections 

 are washed quickly in distilled water and placed in strong alcohol, 

 where the color is washed out until the desired degree of intensity 

 is reached. They are now ready for mounting in glycerine, or, 

 if desired, they may be placed inxylol and then mounted in balsam. 

 If the sections are so deeply stained that they cannot be suffi- 

 ciently washed out in alcohol, they should be placed for a time 

 in a 2.5 per cent, solution of tannin. 



