294 CYTOLOGICAL METHODS. 



test, for the intensity of the coloration it produces varies greatly in 

 different nuclei, and may in certain nuclei be extremely weak, or 

 (apparently) even altogether wanting. In these cases other tests 

 must be applied in order to establish with certainty the presence or 

 absence of that element. 



Chromatin is distinguished from albuminoids by not being soluble, 

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

 hydrochloric acid. It is easily soluble in concentrated mineral 

 acids, in alkalies, even when very dilute, and in some alkaline salts, 

 such as carbonate of potash and biphosphate of soda. In the 

 presence of 10 per cent, solution of sodium chloride it swells up into 

 a gelatinous mass, or even, as frequently happens, dissolves entirely 

 (CARNOY, Biol. Cell, pp. 208 9). It is only partially digestible 

 (when in situ in the nucleus) in the usual laboratory digestion fluids. 



The solvents of chromatin that are the most useful in practice 

 are 1 per cent, caustic potash, fuming hydrochloric acid, or cyanide 

 of potassium, or carbonate of potash. These last generally give 

 better results than dilute alkalies. They may be employed in 

 solutions of 40 to 50 per cent, strength. If it be desired to remove 

 all the chromatin from a nucleus the reaction must be prolonged, 

 sometimes to as much as two or three days, especially if the opera- 

 tion be conducted on a slide and under a cover-glass, which is the 

 safer plan. 



These operations must be performed on fresh cells, for hardening 

 agents render chromatin almost insoluble in ammonia, potash, or 

 sbdic phosphate, etc. Hydrochloric acid, however, still swells and 

 dissolves it, though with difficulty. 



Chromatin resists the action of digestive fluids much longer than 

 the albumins do ; so that a moderate digestion serves to free the 

 chromosomes from any caryoplasmic granulations that may obscure 

 them, whilst at the same time it clears up the cytoplasm. UNNA 

 (Monatschr. prakt. Derm., xxxiii, 1901, p. 342) digests tissues in 

 solutions of sodium chloride, to remove the granoplasm. See 

 also 652, 664 and 668. 



Glycogen. 



646. Glycogen is a carbohydrate which occurs in many cells, 

 both glandular and genital : it is found in both inter- and intra- 

 cellular positions, in the form of small areas of flocculent appearance. 

 For its study in a tissue or organ two methods should be used : 

 (1) An iodine technique ; and (2) that of Best's carmine. The 

 specificity of the latter method has been questioned, and both 

 techniques must be used for comparison (see p. 338). 



