NORMALS, MICROSCOPICAL 



175 



NUCLEASE 



normal can be returned with greater 

 assurance. This is particularly true 

 for the blood and cerebrospinal fluid. 

 Histological criteria of normality are 

 also of some value in the examination of 

 joint fluids, serous fluids and vaginal 

 smears. 



Normoblasts (orthochromatic erythro- 

 blasts). Stage in formation of erythro- 

 cyte between erythroblast and reticulo- 

 cyte ; nucleus spherical or oval, picnotic, 

 often excentrically placed. Cytoplasm 

 contains much hemoglobin, not nor- 

 mally present in circulation. See 

 Erythrocytes, Developmental series. 



Nucleal Reaction is a microchemical test 

 for Thymonucleic Acid which see, also 

 Feulgen Reaction. 



Nuclear Inclusions are characteristic of 

 some virus diseases but in many such 

 diseases they are not found. Only 

 when they are present in large numbers 

 as in yellow fever is it feasible to in- 

 vestigate them in fresh tissues. Stain- 

 ing reactions, solubility tests and other 

 properties of fresh inclusions are de- 

 scribed by Cowdry, E. V. and Kitchen, 

 S. F., Am. J. Hygiene, 1930, 11, 227-299. 

 Methods for their identification in fixed 

 tissues are summarized by Cowdry, 

 E. v.. Am. J. Clin. Path.. 1940, 10, 133- 

 148. For general purposes fixation in 

 Zenker's fluid, paraffin imbedding and 

 coloration with Hematoxylin and Eosin 

 is the most satisfactory. Coloration 

 with Phloxine or Eosin Methylene blue 

 gives more brilliant colors but they fade 

 more rapidly. The nuclear inclusions 

 are typically acidophilic and therefore 

 take eosin and phloxine energetically. 

 When it is desired to reverse the colors 

 use Safranin-Light Green which gives 

 green inclusions and red chromatin. 

 For microchemical methods see Cowdry, 

 E. v., Science, 1928, 68, 40-41, see also 

 Specific Gravity determinations. Paper 

 by Lucas, A. M., Am. J. Path., 1940, 

 16, 739-760. 



When the following features are noted 

 in a section it is likely that a virus has 

 been at work : 



1. A considerable number of inclu- 

 sion-laden nuclei which can be arranged 

 in series representing stages in develop- 

 ment. This indicates an active process 

 in which the nuclei exhibiting the most 

 advanced alterations were affected first 

 and the others in succession. 



2. A change in which the accumula- 

 tion of acidophilic material, forming 

 the inclusion, is accompanied by mar- 

 gination of basophilic chromatin on the 

 nuclear membrane, a disappearance of 

 nucleoli and ultimate death and disin- 

 tegration of the cells. This suggests 

 that the inclusion formation is not 



merely an intranuclear heaping up of 

 material effected without injury. 



3. A cellular reaction characterized 

 by hyperplasia, hypertrophy or necrosis. 



Nuclear inclusions are of two general 

 sorts — A and B (Cowdry, E. V.,Arch. 

 Path., 1934, 18, 527-542). Type A are 

 the most definite and exhibit the proper- 

 ties noted above under 2. When the 

 basophilic chromatin does not marginate 

 on the nuclear membrane and the 

 nuclear structure does not disintegrate 

 — we have to proceed warily. Such 

 inclusions (type B) are droplet-like 

 masses of acidophilic material sur- 

 rounded by clear halos. They have 

 been reported in Borna disease, in polio- 

 myelitis and in several other conditions. 

 When observed in routine preparations 

 they are seldom conspicuous structures. 

 It is only when stronglj^ 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 crj's- 

 talline structure are not so well shown 

 in fixed and stained preparations. The 

 inclusions give the usual protein reac- 

 tions but arc Feulgen negative. The}' 

 apparently contain virus. 



An interesting and well illustrated 

 account of intranuclear parasites is pro- 

 vided bj' H. Kirby, Jr. in Calkins, G. X. 

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

 logical Research. New York: Colum- 

 bia University Press, 1941, 1148 pp. 

 Nuclease. This enzyme acting on nuclcins 

 is very elusive. A. Van Herwerden has 

 described it in several publications, of 

 which the most recent is Anat. Anz., 

 1914, 47, 312-325. Lison (p. 175) refers 

 to two other papers by Sachs and Oes 

 but does not give references to them. 

 If one could rely on digestion of sections 

 for two days at 37 °C. removing all 

 nucleins to the exclusion of all other 

 cellular materials an important path 

 for investigation would be opened up. 

 A purified nuclease is required. Sec 



