SPECIAL METHODS. 189 



commended especially by Strasburger, may often be used 

 with good results. But very weak solutions of the dye must 

 generally be used. Examination may be made in the stain 

 itself or in glycerine. The preservation of preparations 

 stained with methyl green is not possible. 



ft. Picro-nigrosin. 



329. The solution of nigrosin in a concentrated aqueous 

 solution of picric acid, recommended by Pfitzer (I), may be 

 used with good results for simultaneous fixing and staining, 

 -especially with algae. In order to remove the chlorophyll 

 at the same time, a solution of nigrosin and picric acid 

 in 96$ alcohol may be used. At least 24 hours' time is 

 usually necessary for good staining. The preparations are 

 then washed in glycerin and may be preserved in glycerine- 

 gelatine. But the stain comes out much more finely in 

 balsam or the like. It is preserved well in either medium. 



d. Staining intra vitam. 



330. The staining of living nuclei was first accomplished 

 in the higher plants by Campbell (I) by means of dahlia, 

 methyl violet, and mauve'in. The author mentioned placed 

 pieces of the objects to be studied in a .001$ to .002$ solu- 

 tion of one of these dyes, and usually left them there for 

 several hours. The stamen-hairs of Tradescantia virginica 

 are recommended as especially adapted for these studies, 

 and Campbell succeeded in staining their nuclei while in 

 process of division. But these stainings are usually pretty 

 faint and always much less differentiated than good stain- 

 ings of fixed nuclei. This staining intra vitam has not led 

 to any important results concerning the morphology of the 

 nucleus. 



