NUCLEI 



177 



NUCLEOLUS 



Proc. Soc. Exp. BioL & Med., 1935, 

 32, 1428-1429). 



The collection of nuclei in bulk for 

 chemical analysis is now feasible (see 

 Centrifugation). Thus nuclei of liver 

 cells can be separated from cytoplasms 

 by centrifugation after treatment with 

 dilute citric acid. Normal liver nuclei 

 do not accumulate P32 while tumor 

 nuclei and regenerating nuclei do 

 (Marshak, A., Federation Proceedings, 

 Baltimore, 1942, 1, (2)57). A method 

 for separating nuclei from rest of thy- 

 mus is described by Williamson, M.B 

 and Gulick, A., J. Cell. & Comp. Phys- 

 iol., 1942, 20, 116-118. The authors 

 analysed the mass of nuclei for calcium, 

 magnesium and phosphorus. Another 

 method for separating from cytoplasm 

 (Crossmon, G., Science, 1937, 85, 250) 

 is to place drop 5% aq. citric acid in 

 center of a slide smeared with Mayer's 

 Albumin Glycerin. Add piece fresh 

 muscle. This slowly becomes trans- 

 parent and infiltrated. The cloudiness 

 of the citric acid is caused by released 

 nuclei. Remove muscle and allow fluid 

 containing nuclei to dry completely. 

 Hold nuclei in place by treating with 

 95% ethyl alcohol. Wash in tap water, 

 then in aq. dest., stain with Mayer's 

 Hemalum, blue in tap water, counter- 

 stain in eosin, dehydrate, clear and 

 mount. Perhaps the technique can be 

 so adjusted that it will permit the sepa- 

 ration of nuclei from other tissues. 

 See Arginase. 



Nucleic Acids, see Desoxyribonucleic, Ribo- 

 nucleic and Thymonucleic. 



Nucleocytoplasmic Ratio. A histological 

 method for computing this ratio is fully 

 described by Cowdry, E. V. and Paletta, 

 F. X., J. Nat. Cancer Inst., 1941, 1, 

 745-759 ; but there are many such tech- 

 niques. A chemical method has been 

 used to advantage by Dawbarn, M. C, 

 Australian J. Exp. Biol. & Med. Sci., 

 1932, 9, 213-226. Her ratio is obtained 

 by dividing the nucleic acid nitrogen 

 by the total coagulable nitrogen less 

 nucleic acid nitrogen. 



Nucieolinus is a term introduced by Ilaeckel 

 to indicate a deeply staining granule 

 within a nucleolus. For details see 

 Champy, C. and Carleton, H.M., Quart. 

 J. Micr. Sci., 1921, 65, 589-610. 



Nucleolus (L. dim. of nucleus) is a body 

 within a nucleus. There are at least 

 three sorts. 



1. Plasmosomes. These can be de- 

 fined as roughly spherical bodies, which 

 can easily be seen in the nuclei of some 

 living cells without the aid of any stains, 

 which stain after appropriate fixation, 

 namely, with plasma or "acid" stains 

 like eosin, (hence the name) and which 



do not directly contribute material 

 to the formation of chromosomes. 



Plasmosomes are not to be confused 

 with cytoplasmic granules called plas- 

 mosomes by Arnold many years ago or 

 with plastosomcs, a term given by 

 Meves to mitochondria and now fortu- 

 nately being discarded. They can be 

 referred to as acidophilic or oxyphilic 

 nucleoli, but sometimes they are tinged 

 quite strongly with basic dyes. They 

 are of dense consistency, easilj^ shifted 

 by centrifugal action and are in some 

 cases more resistant to the digestive 

 action of pepsin and hydrochloric acid 

 than karyosomes. 



2. Karyosomes, are by contrast in- 

 tensely basophilic and do contribute 

 material to the making of chromosomes 

 during mitosis. But they are resistant 

 to peptic hydrochloric acid digestion. 

 Wilson (E. B., Heredity, New York: 

 Macmillan 1925, p. 93) recognizes 3 

 types, net-knots, chromosome-nucleoli 

 and karyospheres. There is doubt about 

 the existence in vivo of the net-knots in 

 the same shape, size and position as 

 observed in stained sections. 

 _ 3. Amphiniicleoli (G. amphi on both 

 sides) are nucleoli consisting of both 

 plasmosome and karyosome material. 

 Often the acidophilic substance acts as 

 a kind of core and the basophilic sub- 

 stance is close to it or appears to be 

 plastered on its surface. The latter may 

 not occur in the same form in the living 

 nucleus. 



The fixation which shows, when the 

 sections are stained, the highest degree 

 of nucleolar detail is not necessarilj' 

 the best (see remarks about Nuclei,). 

 The Linin network, net-knots and 

 basophilic material marginated on plas- 

 mosomes may result in part from the 

 coagulating action of the fixative on 

 inaterial originally distributed diffusely 

 in the nucleoplasm. Nucleoli which 

 look bubbly, or are surrounded by halos, 

 are to be regarded with suspicion. 

 Fixation in Acetic-Osmic-Bichromate 

 and in other fluids containing osmic 

 acid is indicated but they penetrate 

 poorly. Staining by almost any tech- . 

 nique which gives a good color contrast 

 between acidophilic and basophilic 

 materials is satisfactory. The classical 

 stain is with safranin and light green. 

 Eosin and methylene blue, hematoxylin 

 and eosin are recommended, likewise all 

 methods advised for Nuclear Inclusions 

 caused by viruses. 



Usually no difficulty is experienced 

 in the identification of nucleoli. How- 

 ever with the plasmosomes there may 

 be some question. In the first place 

 nuclear inclusions type B (Cowdry 

 E. v., Arch. Path., 1934, 18, 527-542) 



