HISTOLOGY OF THE THYMUS 311 



If a very weak solution of tlie dye be used, the nucleus remains 

 unstained, but with a stronger concentration takes a distinct 

 purplish-red tinge. It is generally held that nuclear staining 

 takes place in dead cells (Plato (18), Fischel (19), Cesaris-Demel 

 (20)). Since we have no absolute morphological criteria for dis- 

 tinguishing a living from a dead cell, it is probably more accurate 

 to say that staining of the nucleus takes place onlj^ in a cell which 

 is dead or injured. The converse is not true, however, and all 

 dead or injured cells do not show nuclear staining with the vital 

 stains.^ 



Now it is certainly possible by means of Janus green to bring 

 about a simultaneous contrast staining of granulae and nucleus 

 in living cells. While I have not observed amoeboid activity in 

 the small cells, nor any other functional indication of life, in the 

 case of other elements which will be described in detail, marked 

 active changes of form took place after staining was completed. 

 The appearance of a reddish color denotes a reduction of the dye- 

 stuff, or in other words a taking up of oxygen on the part of the 

 nucleus, and is in all probability in itself an indication of via- 

 bility on the part of the nucleus. The recent experiments of 

 Warburg and Meyerhof (24) which show that crushed fragments 

 of sea-urchin eggs and even acetone extract powders are capable 

 of taking up oxygen for several hours, perhaps weakens the force 

 of this argument. More convincing is the fact that dead nuclear 

 material which is taken up by phagocytic cells, stains greenish 

 blue and not reddish. 



^ To this general rule that staining of the nucleus indicates death or injury to 

 the cell, there are a few exceptions noted in the literature. Thus Przemicki (21), 

 working with certain Protozoa (Opalina, Nyctotherus) succeeded in staining the 

 nucleus in individuals the motility of which was preserved for five days and in 

 which cell division occurred. Goldman (22) in a recent paper states that he has 

 succeeded in vitally staining the nuclei of liver cells. Kite and Chambers (23) 

 announce in a preliminary note that they have produced a differential staining 

 with Janus green of the chromosomes in the spermatic cells of the squash-bug, 

 crickets and grasshoppers, and they have followed the transformation of ana- 

 phase to telophase in a stained spermatocyte. In some observations made by 

 the writer in collaboration with Dr. R. A. Lambert, upon dividing cells of chick 

 embryos in vitro, it was found that the chromosomes were stained red by Janus 

 green, but that division of the cells was arrested upon the addition of the dye. 



