THE INTERPHASE NUCLEUS 



several points of view to inquire what happens to these bodies in 

 the interphase nucleus. Nobody since the advent of the chromosome 

 theory of heredity has doubted that the chromosomes in the interphase 

 nucleus are 'there' in some sense, although with White^ one might 

 regard them as 'unfixable'. 



Until recently, it seemed unlikely that any general answer would be 

 possible to the question of the form of the chromosomes in interphase, 

 for the differences between the fixed and the living nucleus seemed 

 irreconcilable. Usually in fixed preparations, the interior of the nucleus 

 is occupied by a complex network; while at the other extreme, the 

 nucleus of the living Echinus oocyte contains a fluid little more viscous 

 than water through which the nucleolus falls readily under gravity 

 (Gray^).* 



Such a comparison served to encourage scepticism on the subject of 

 the detail seen in the fixed nucleus, which was further reinforced by 

 reports of the apparent 'optical emptiness' of the nuclei of living cells 

 in tissue cultures, when seen either in the bright-field or the dark-field 

 of the microscope (Lewis and Lewis, ^ Strangeways and Canti^). 

 Insufficient weight was then accorded to descriptions of visible texture 

 in plant nuclei in life (p 72) and the observation of Flemming' was 

 long forgotten that the 'Geriiststrange' seen in a living amphibian 

 nucleus are only brought out more sharply on the addition of a fixative. 



The conclusion that the detail seen in the nuclei of tissue cultures 

 after fixation was spurious was reinforced by the observations of 

 Lewis (M.R.)* that a 'mass of granules' appeared within them when 

 an acid was added to the culture medium. This gelation was reversible 

 and the usual appearance and behaviour of the cell was resumed when 

 the normal pH was restored. 



We now know that the failure to detect structure within the nucleo- 

 plasm of such cells lay with the method of observation, and that in fact 

 the nucleoplasm of such nuclei is not a 'perfect and absolute blank'. 

 The ordinary bright-field microscope is insufficiently sensitive to fine 

 detail; the dark-ground method which brilliantly illuminates sharp 

 discontinuities at surfaces and boundaries, does not scatter light in 

 regions where there are only fine gradations in refractive index. 

 Observations by phase contrast of the living nucleus of cells in tissue 

 cultures in which such fine detail is revealed have been described by 

 Fell and Hughes,^ Comparison of the appearance of the same nucleus 

 in life and after fixation should be extended to other material. Such 

 observations were first made by Tellyesniczky^^ who observed how 

 much the texture of the fixed nucleus can vary with the nature of the 



• If the chromonemata of the Echinus oocyte Hne the inside of the nuclear membrane, as 

 is true of other nuclei, they would not impede the fall of the nucleolus through the nuclear 

 sap. 



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