CHEMISTRY OF THE LIVER. 303 



and a sharp chemical differentiation between the two com- 

 ponent parts of the cells is not yet possible, however simple 

 the microscopic differentiation may be. But some points have 

 been worked out and these will be briefly referred to. 



The Nucleus. The most important chemical constituent 

 of the nucleus is the complex protein substance known as 

 nuclein, already referred to in an earlier chapter. Nucleins 

 of different character are obtained from different sources. 

 These nucleins exist in combination as nucleo-proteids, and in 

 turn break up into nucleinic acids and a protein fraction, which 

 was explained in the chapter referred to. The cell nucleus 

 appears to consist very largely if not wholly of the nucleo- 

 proteid. On digestion with pepsin and hydrochloric acid the 

 nuclein is separated and may be purified by washing with 

 water, dissolving in very weak alkali and reprecipitating with 

 acid. The pure nuclein is a white amorphous substance which 

 gives the Millon test and the biuret test. The various nuclein 

 substances in cells are characterized by a strong affinity for 

 dye stuffs, especially for some of the coal tar dyes ; this prop- 

 erty is utilized in the microscopic examination of tissues. 

 Nuclein fused with sodium carbonate and nitrate yields phos- 

 phate, but heated without the alkali an acid residue (meta- 

 phosphoric acid) is left. 



By various decompositions nuclein substances yield a num- 

 ber of peculiar basic bodies kno\vn as the xanthine or purine 

 bases, which will be considered in a following chapter. The 

 cell nucleus contains in combination a number of metallic ele- 

 ments among which iron is perhaps the most important. 

 Potassium salts are present, while those of sodium are present 

 only in traces, if at all. 



The Protoplasm. This soft spongy portion of the cell 

 consists largely of water. The solid part, making up 10 to 20 

 per cent usually , contains several albumins proper and proteids. 

 Lecithin is an important and relatively abundant constituent 

 of the protoplasm. Its presence seems to be intimately asso- 

 ciated with phenomena of reproduction and building up of 



