CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 211 



with Bouin's fluid), Pappenheini's stain and Mann's methyl-blue- 

 eosin method. Ludeord {Jour. Roy. Mic. Soc, 1922, p. 113) 

 obtained his best preparations after fixing with corrosive acetic 

 and staining with Mann's stain. In the oocytes of molluscs he 

 found that both the oxyphil and basophil nucleoli gave a negative 

 reaction with the Feulgen test (Proc. R. S. B., cii, 1928). 



In studying nucleoli one should use more than one set of stains 

 and also other methods outlined below. 



The impregnation methods of Cajal, or of Da Fano, may prove 

 very useful. 



There are a number of reagents which react differentially upon 

 chromatin and plastin, enabling one to separate these two 

 chemically. One of the simplest, and according to Saguchi the 

 most satisfactory, is to fix the tissue in absolute alcohol and after 

 washing place it in a 0-1 per cent, solution of potassium hydroxide. 

 Even after two to four minutes most of the chromatin will be 

 dissolved while the plasmosome will not be affected. After 

 longer treatment, the tissue can be imbedded and sections stained 

 in the ordinary way. (See Saguchi, Zytologische Studieti, Hefte 

 vii, 1934. Other methods are also described in this paper and 

 pertinent literature cited.) 



Zirkle has developed several fixatives designed to aid in dis- 

 tinguishing nuclear components. (See especially, Cytologia, ii, 1931, 

 p. 85. for formulae and literature.) The following solution is said 

 to fix plastin and destroy chromatin : Potassium bichromate 

 1-25 to 1-5 grm., ammonium bichromate 1-25 to 1-5 grm., sodium 

 chroma te 1-0 to 0-5 grm., and aq. dest., 100 c.c. 



647. Centrosomes. These structures are relatively easy to 

 preserve. Among the fixatives generally employed are Bouin's 

 and Flemming's fluids and sublimate combinations. Tissue 

 should be thoroughly washed after fixation and very thin paraffin 

 sections are advisable. The best method of staining, so far 

 developed, is iron hsematoxylin. Thin sections should be 

 mordanted in fresh 2-5 per cent, ferric alum for twelve to twenty- 

 four hours and stained in ha?matoxylin for several days. Counter- 

 staining with acid fuchsin or light green is often helpful. Mallory's 

 phosphotungstic acid hsematoxylin is recommended by 

 Sturdivant {Jour. Morph., xlv, 1933, p. 435) as the best progressive 

 hsematoxylin stain. The practice of Heidenhain of staining 

 tissue first in Bordeaux R., and then in iron hsematoxylin, seems 

 no longer to be followed. 



* 642. Zirkle {Science, May, 1937) recommends for permanent 

 mounting the following : — Acetic acid (glacial) 50 c.c., water 50 c.c, 

 glycerin 1 c.c, gelatin (powdered) 10 grm., dextrose 4 grm., FeClj 

 05 grm., carmine to saturation. Dissolve gelatin in water, add 

 other components, boil, filter. Use as ordinary aceto-cannine, or 

 dilute in various proportions with Belling's aceto-carmine. 



