CHAPTER XXVI. 311 



been investigated. Even if part of these nucleoli did stain green 

 in acidulated methyl green, it would be unsafe to interpret such 

 material as chromatin, especially in view of the fact that methyl 

 green will stain silk and mucin, and the secretions of many gland 

 cells ; plasmosomes often seem to be related in some way to gland 

 secretion. 



Most of the work on plasmosomes or true nucleoli has been 

 carried out on fixed material, and it cannot be too strongly emphasised 

 that by such means it is not possible properly to discriminate between 

 what is true chromatin, and what is not true chromatin. There are no 

 perfectly specific chromatin dyes known, the nucleoli in general 

 may be made to stain differently according as to whether they may 

 have been fixed in acid or non-acid fixatives (this applies especially 

 to acetic acid), or in osmicated or non-osmicated mixtures, while 

 true chromatin may itself stain " acidophile," as, for instance, in 

 the head of the sperm during spermateleosis, and in the egg during 

 oogenesis. 



These remarks refer also to the use of so-called specific dyes for 

 discriminating between and identifying the various cytoplasmic 

 inclusions. See especially 707 et seq. 



The case of the so-called karyosome or chromatin nucleolus is 

 even less satisfactory ; one often meets with " solid " intra-nuclear 

 bodies which stain basophil with many so-called nuclear dyes, but 

 which are only doubtfully to be regarded as chromatin. In this 

 connection, see Bayliss ( 204) on specificity of dyes. 



Safranin and light green, and iron hsematoxylin, following 'strong 

 Flemming's fluid, are classic stains for nucleoli, but neither of these 

 methods is to be regarded as providing any useful evidence as to the 

 micro-chemical nature of the bodies they tinge. They simply stain 

 most deeply, solid bodies. 



The relationship between nucleoli and the chromatin network is quite 

 unknown in general, but CAJAL and CARLETON (for references see 

 Quart. Jour. Micr. 8ci, Ixiv, 1920) have shown by formalin and silver 

 nitrate methods that both basophil and oxyphil nucleoli may contain 

 an argeiitophile core. Carleton has followed the core through mitosis, 

 and finds that it keeps its individuality ; the definitive nucleolus of the 

 " resting " nucleus is possibly derived after every mitosis from the core 

 or nucleolinus. - 1 have found nucleolini in the nucleoli of the gut cells 

 of Saccocirrus, and in foUicle -cells of the ovary of insects ; nucleolini 

 are known in many kinds of vertebrate cells. 



For the study of nucleoli the following methods are advised : 

 (1) Fixation by a corrosive sublimate, both acidified by acetic acid, 

 and alone. (2) Fixation by hot water or steam. (3) Fixation by a 



