570 Douglas H. Campbell. 



cells have been successfully colored. Pfeffer i) mentions that Heidenhjlix 

 found that the epithelial cells of the urinary tubes were colored by indigo- 

 carmine when this was injected into the blood, the nucleus especially being 

 deeply colored. Dreser 2] reached similar results in the kidneys of the frog 

 with acid-fuchsin , Bordeaux-red and acid-violet, Brandt 3) was able to 

 obtain a faint coloring of the nucleus in amoebae and heliozoa with haema- 

 toxylin; and La Valette *) succeeded with dahlia in coloring the living 

 spermatozoids of Bombinator igneus, and the nucleus and para-nucleus of 

 the living spermatocysts of Blatta germanica., both resting nuclei and the 

 division-stages. 



Of the various colors employed by these observers, only one, dahlia, 

 has given satisfactory results with vegetable cells. By its use the first un- 

 questionable coloring of the living nucleus was observed by me in the sta- 

 men-hairs of Tradescantia Virginica, which proved to be an excellent sub- 

 ject for experiment. Farther search, however, extended the number of 

 cases very much; and it was also found that in many instances methyl- 

 violet and mauvein, especially the latter, gave quite as good results as dahlia. 



In all cases of successful coloring both the nucleus and the protopiasm 

 appear perfectly normal, there being no dlstortion or contraction, and the 

 protoplasmic Streaming continuing. The intensity of the color varies much 

 in different instances both with the State of the nucleus and the time of 

 Immersion in the staining fluid. 



Of course in selecting cells for study such should be chosen that have 

 thin, uncuticularized walls, as the penetration of walls with a thick cuti- 

 cle is difficult and the walls themselves are apt to take up the color. It is 

 also desirable, of course, to have some sure means of determining whether 

 the cell is still alive; and as the readiest means of doing this, cells were 

 selected in all cases in which there was evident protoplasmic Streaming, 

 or, as in the case of spermatozoids, ciliary movement. As long as unmista- 

 keable movement of the protopiasm can be detected it is of course certain 

 that the cell is still alive. 



Methods used. 



As yet but three colors, dahlia, methyl-violet, and mauvein, have been 

 found that certainly colored the nucleus in the cells examined, and these 

 three are much alike in their color and properties, though differing mate- 

 rially in chemical composition. All of them are violet-purple aniline colors, 

 readily soluble in water. 



In making the experiments a Solution of the coloring agent in filtered 

 rain-water was made. For ordinary use at -1^ Solution was found conve- 



1) I.e. page 269. 2) ibid. 3) ibid. 



4) Strasbürger, Bot. Prakt. II. edition. p. 630. 



