STAINING. 187 



Congo red, neutral red, Nile blue, Janus green, and, under 

 certain conditions, dahlia and eosin, gentian violet, with 

 perhaps methyl violet, and some others. 



These reagents are best employed in a state of consider- 

 able dilution, and in neutral or feebly alkaline solution 

 acids being of course toxic to cells. Thus employed, they 

 will be found to tinge with colour the cytoplasm of certain 

 cells during life ; never, so far as I can see, nuclear chromatin 

 during life ; if this stain, it is a sign that death has set in. 

 The stain is sometimes diffused throughout the general sub- 

 stance of the cytoplasm, sometimes limited to certain granules 

 in it. 



It has been asserted by some observers that the nucleus 

 may be stained during the life of the cell by means of 

 Bismarck brown, Congo red, methylen blue, neutral red, 

 Nile blue, and safranin. But it is by no means clear from 

 the statements of these writers that the coloration observed 

 by them is localised in the chromatin of the nucleus. It 

 would rather appear to be a diffuse coloration brought about 

 by mechanical and momentary retention of the dye in the 

 nucleus which is a very different thing from a true nuclear 

 stain. And in some of the cases reported it is by no means 

 certain that the coloured nuclei were really in the living 

 state. See hereon the article by FISCHEL (" Farbungen, 

 intravitale ") in Encycl. mik. Tecknik. 



I have myself made a considerable number of observa- 

 sions on the subject of intra-vitam staining, and have come 

 to the same conclusion as GALEOTTI (Zeit. wis*. Mik., xi, 

 1894, p. 172), and many recent writers, namely, that most 

 of the so-called i( intra-vitam " stains are either not true 

 stains or that the stained substances are not really living. 

 The coloration appears mostly, if the cell that shows it has 

 remained in a state of unimpaired vitality, to be due to 

 simple absorption or imbibition of the colouring matter 

 by the cell, not to a molecular combination of the colouring 

 matter with any of the constituents of the cells. 



And when a more or less fast stain has been obtained, it 

 is generally found that this is limited to cell-contents that 

 do not appear to form an integral part of the living texture 

 of the cell to food-granules, or katabolic products, or tho 

 like. 



