NUCLEASE 



17€ 



NUCLEI 



Barnes, J. M., Brit. J. Exp. Path., 1940, 

 21, 264-275 for analysis of nuclease in 

 lymphocytes and polymorphonuclear 

 leucocytes. 

 Nuclei. To look into the body and study 

 the nuclei of living cells is feasible 

 only up to a certain point. The ob- 

 servation of the Clarks' (E. R. and E. 

 L., Am. J. Anat., 1936, 59, 123-173) 

 that in transparent chambers inserted 

 into the ears of rabbits (Sandison's 

 Technique) the finely granular leuco- 

 cytes may be followed about and seen 

 to lose their nuclear polymorphism is 

 significant of what can be done. In 

 Tissue Cultures the cells are living 

 under less natural conditions but they 

 grow in thin films and can therefore be 

 observed at high magnification. Care- 

 ful analysis of moving pictures, show- 

 ing nuclear form and structure, like 

 those of Dr. W. H. Lewis distributed 

 by the Wistar Institute, can prove very 

 fruitful. By ultracentrifugation data 

 can be obtained bearing on intranuclear 

 Viscosity and the relative Specific 

 Gravity of nuclear components. The 

 techniques of Microdissection and 

 microinjection also offer opportvmities 

 for advance. The Vital Staining of 

 nuclei without killing the cells is diffi- 

 cult and not particularly helpful (Acri- 

 flavine); but it appears to be feasible 

 in a variety of vertebrate cells with 

 dilute solutions of methylene blue 

 (Russel, D. G., J. Exp. Med., 1914, 20, 

 545-553), in amebae by microinjection 

 (Monne, L., Proc. Soc. Exp. Biol. R. 

 Med., 1934-35, 32, 1197-1199), and in 

 the fibroblasts of tissue cultures with 

 crystal violet (Bank, O. and Kleinzeller, 

 H., Arch. f. exp. Zellf., 1938, 21, 394- 

 399). The same can be said for Ultra- 

 violet Photomicrography. 



The choice of fixative is important. 

 It is difficult to secure after formalin 

 fixation a brilliant color contrast of 

 basophilic and acidophilic nuclear mate- 

 rials by staining with Giemsa, Eosin- 

 Methylene Blue and other mixtures of 

 "basic" and "acid" dyes, because the 

 former take very intensely and the 

 latter, lightly. But following Zenker's 

 fluid and other mixtures containing 

 potassium bichromate, which acts as a 

 sort of mordant, these stains color the 

 acidophilic as well as the basophilic 

 components. It is for this reason, and 

 because nuclear inclusions caused by 

 virus action are usually acidophdic, 

 that formalin used alone is contraindi- 

 cated as a fixative. 



On the morphological side it is known 

 that nuclei stained in sections after 

 fixation in the usual ways show a di- 

 versity, or heterogenicity, of internal 

 structure which cannot be observed by 



the most careful examination of the 

 nuclei of living cells. In the latter only 

 the nucleolus can generally be distin- 

 guished. The so-called linin network, 

 and small irregular particles staining 

 with acid and basic dyes, are not ob- 

 served. These probably result from the 

 coagulating action of the fixative upon 

 materials present in solution or fairly 

 uniformly distributed in the nucleo- 

 plasm. Stained sections of tissues fixed 

 in fluids containing fair amounts of 

 osmic acid (Altmann's Mixture and 

 Bensley's Acetic-Osmic-Bichromate) 

 exhibit, on the contrary, nuclei with 

 quite homogeneous looking nucleoplasm, 

 containing nucleoli, which portray the 

 condition in vivo more accurately. 

 Colored illustrations of the nuclei of 

 liver cells containing inclusions after 

 osmic and non-osmic fixation (Figs. 47 

 and 20) are provided by Cowdry, E. V. 

 and Kitchen, S. F., Am. J. Hyg., 1930, 

 11, 227-299. This does not mean, 

 however, that the ground substance is 

 always optically homogeneous in vivo. 



The shrinkage of nuclei when exam- 

 ined in stained sections is generally 

 more than 10% of their size in vivo. 

 In post-mortem autolysis, particularly 

 of the kidney, one of the first nu- 

 clear modifications is shrinkage. The 

 shrunken nuclei may stain intensely 

 with both basic and acid dyes. The 

 acidophilic material in them may even 

 appear to be increased; for it is more 

 concentrated, owing to decrease in 

 volume (oxy chromatic degeneration). 

 They are also more spherical and less 

 oval in shape. In early stages this 

 modification can easily be identified 

 by its occurrence in some tubules and 

 not in others. A comparable hyper- 

 chromatism of nuclei at the edge of a 

 section accompanied by a flattening of 

 them may indicate that a surface film 

 of tissue was permitted to dry before 

 fixation. 



Among the stains Iron Hematoxylin 

 is a favourite because of its sharpness 

 and permanence. Phloxin-Methylene 

 Blue is also recommended. If one de- 

 sires to reverse the colors and get red 

 nuclei and green cytoplasm Safranin 

 Light Green is suggested. The 

 Safranin-Gentian Violet-Orange G 

 technique gives several beautiful color 

 tones. Recently the Feulgen reaction 

 by which Thymonucleic Acid can be 

 demonstrated has become very popular 

 as the most sharply discriminating 

 nuclear stain. Microchemical studies 

 are now possible which a few years ago 

 were undreamed of. The method of 

 Microincineration reveals some of the 

 mineral constituents (Scott, G. H., 



