NUCLEASES 



238 



NUCLEI 



It is only when strongly stained with 

 fuchsin, for instance, that they catch 

 the eye. Perhaps careful search of 

 tissues not subjected to virus action 

 might reveal similar bodies. Therefore 

 in the case of type B inclusions, insist- 

 ence on criteria 1 and 3 is desirable. 

 The nuclear inclusions in the liver 

 following severe burns look very much 

 like those caused by viruses (Belt, T. 

 H., J. Path, and Bact., 1939, 48, 493- 

 498). 



In plants, as in animals, some nuclear 

 inclusions are indicative of the action 

 of certain viruses, see excellent sum- 

 marizing account by Bawden, F. C, 

 Plant Viruses and Virus Diseases. 

 Waltham: Chronica Botanica Co., 1943, 

 294 pp. Since the inclusions usually 

 occur in the form of "thin flat crystal- 

 line plates" they should be examined in 

 living cells in the dark field and in 

 polarized light because details of crys- 

 talline structure are not so well shown 

 in fixed and stained preparations. The 

 inclusions give the usual protein reac- 

 tions but are Feulgen negative. They 

 apparentl}' contain virus. 



An interesting and well illustrated 

 account of intranuclear parasites is pro- 

 vided by H. Kirby, Jr. in Calkins, G. N. 

 and Summers, F. M., Protozoa in Bio- 

 logical Research. New York: Colum- 

 bia University Press, 1941, 1148 pp. 

 Nucleases — Written by E. W. Dempsey, 

 Dept. of Anatomy, Washington Uni- 

 versity, St. Louis. February 26, 1951 — 

 For many j-ears, cytologists have at- 

 tempted to apply enzjane preparations 

 which chemically degrade or destroy 

 nucleic acids. Van Herwerden, A., 

 Anat. Anz., 1914, 47, 312-325, and Lison 

 (p. 175) describe the older experiments. 

 Until recently, however, the enzyme 

 preparations were contaminated with 

 trypsin and other proteolytic enzj'mes, 

 so that the results after digestion of 

 sections with nucleases were difficult to 

 interpret. Kunitz, M., J. Gen. Phys- 

 iol., 1940, 24, 15-32 described the prepa- 

 ration of crystalline ribonuclease, an 

 enzyme which depolymerizes and there- 

 fore solubilizes pentose-nucleic acid. 

 McDonald, M. R., J. Gen. Physiol., 

 1948, 32, 39-42, reported that the last 

 traces of proteolytic activity in this 

 preparation could be removed by heat 

 treatment. Ribonuclease has been 

 widely used to identify many basophilic 

 cytoplasmic components (Nissl sub- 

 stance, ergastoplasm of pancreatic cells, 

 basophilic inclusions in placenta, cyto- 

 plasmic basophilia in general), and 

 nucleoli in some but not all cells fail to 

 stain after digestion in the enzyme. 

 Desoxyribonuclease, an enzyme which 



depolymerizes desoxypentosenucleic 

 acids, has also been crystallized by 

 Kunitz, M., J. Gen. Physiol., 1950, 

 33, 349-362. This preparation de- 

 stroys the stainability of chromatin, 

 but has not yet had as wide an applica- 

 tion to cytology as had had ribo- 

 nuclease. These preparations are 

 available through the Worthington 

 Biochemical Laboratories, Freehold, 

 N.J. 

 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 poljonorphism 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 opportunities 

 for advance. The Vital Staining of 

 nuclei without killing the cells is diffi- 

 cult and not particularly helpful (Acri- 

 fiavine); 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 



