CHROMATIN, ANIMAL CHROMOSOMES, NUCLEOLI 261 



to a temperature of 60° C, a temperature whieh should be main- 

 tained throughout liydrolysis. A water bath will help to keep 

 the temperature constant, and a variation of a degree or two 

 will not materially alter the result, especially with fixatives 

 requiring longer treatment. The slide, after hydrolysis, is dipped 

 into some of the dilute cold acid solution and then rinsed in 

 distilled water. 



Staining should be carried out for one hour, according to Bauer, 

 in fuchsin-sulphurous acid. This is prepared as follows : Bring 

 200 c.e. of distilled water to a boil, then add 1 grm. of basic fuchsin 

 and stir well. Allow to cool to about 50° C. and then filter. Add 

 20 c.e. of the NHCl and when the temperature reaches about 

 25° C. put in 1 grm. of anhydrous sodium bisulphite. Sulphur 

 dioxide is given off and the liquid slowly turns yellow. Allow to 

 stand for twenty-four hours before using, and keep the bottle well 

 stoppered and in the dark. 



Washing. The stained slides should be passed through three 

 washings containing sulphurous acid. Make up the following 

 solution for this purpose : — 



Distilled water . . . . . . 200 c.e. 



10 per cent, anhydrous sol. sodium bisulphite . 10 ,, 

 Dilute hydrochloric acid . . . . 10 ,, 



The slides are next rinsed in distilled water, counter-stained in 

 light green, if desired, and mounted in damar after dehydration 

 and clearing in the usual way. 



We find that by this method chromatin is stained a bright 

 reddish-purple colour. Plasinosomes (or at least plastin) do not 

 stain except with the counter stain. In animal cells cytoplasmic 

 inclusions do not stain, but in plant tissue such substances in the 

 cell walls as lignin, suberin or cutin may give a positive reaction. 

 On the other hand, it is not certain that chromatin always reacts 

 positively to Feulgen's test. In the young oocytes of some animals 

 the nucleus fails to give an indication of chromatin by this method 

 while the surrounding follicle cells show deeply stained nuclei. 

 Such cases have been interpreted in two ways. Some hold that 

 the chromatin undergoes changes in chemical composition and 

 so does not form aldehydes, others think that the chromatin is 

 physically too dispersed to be easily seen. Those interested in 

 this phase will find much pertinent literature cited in a recent 

 article by Gardiner {Quart. Jour. Micro. Sci., Ixxxvii, 1935, 

 p. 523). 



Literature. Feulgen, R., Ahderhnlden, Hand, der biol. Arbeit. Abt. 

 V. Lief., 213, 1055—1073 ; Ludford, R. J., Proc. U.S., 1927 ; Verne, 

 J., Bull. d'Hist., 1927, 4, 110—122 ; Wermel, E., Zeit. f. Zellforsch. u. 

 mikroskop. Anal., 1926, 4, 227 — 232. 



Chromatin is distinguished from albuminoids by not being soluble, as 

 these are, in water and in weak mineral acids, such as 01 per cent. 



