310 CYTOLOGICAL METHODS. 



the chromatic " blushes ' which are sometimes found surrounding 

 the nuclei of eggs and other cells are sometimes believed to be 

 chromatinic, but the evidence for this is very slender. Chromatin, 

 moreover, may sometimes stain oxyphil, and it is now a well-known 

 fact that the nature of the fixation and the method of staining are 

 important factors in deciding whether the bodies in question will 

 stain in the basic or the acid dye. Under " Nucleoli " are given a 

 number of staining and fixing methods which may be tried. See 

 also Chapter XI, 211. 



667. "Vital" Staining of the Nucleus. A. M. PRZESMYCKY 

 (C. R. Soc. Biol. 3 Ixxviii, 1915) uses neutral red. The living nucleus 

 is said to have a greater affinity for neutral red than protoplasm, as 

 it stains more strongly and decolourises more slowly. This is not 

 my experience with weak neutral red. CHAMBERS (Science, 1912) 

 uses janus green, which shows both chromosomes and spindle 

 fibres. Certain physiologists doubt whether the living resting 

 nucleus can be stained ; some observations on this will be found in 

 Chapter XL, 207. Reference may be made to the paper of P. G. 

 SHIPLEY (Amer. Journ. PhysioL, xlix, 1919). 



It has been asserted by some observers that the nucleus may also 

 be stained during the life of the cell by means of Bismarck brown, 

 Congo red, methylen blue, Nile blue, and safranin. But Bolles 

 Lee believes that 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. In any case there is no dye known which is a specific intra- 

 vital test for chromatin. It seems probable that the most " specific ' 

 test for chromatin known to cytology is acidulated methyl green, 

 for which, see 278 and 645. 



668. Nucleoli. The word is nowadays generally used to mean 

 any large rounded stainable body in the nucleus. The plasmosom'e 

 is " acidophilous " in so far as, in fixed material, it selects the acid 

 dye or dyes from mixtures such as the Ehrlich-Biondi, which stains 

 it reddish or orange. So far as known true plasmosomes of unfixed 

 cells do not stain green with the acid methyl green, but while this 

 may hold for the plastin nucleoli of somatic cells in general, there 

 are to be found in eggs complicated nucleoli which have not properly 



