CHEMISTRY OF THE CELL NUCLEUS 



By W. D. HALLIBURTON, M.D., F.R.S. 



The cell-theory put in the briefest possible way teaches that 

 the unit of structure, both in animals and plants, is a little 

 lump of living material or protoplasm ; the differences between 

 the animal and the vegetable units are of subsidiary importance, 

 though it was the greater prominence of a firm membrane on 

 the exterior of the vegetable unit that led botanists, who were 

 earliest in the field, to adopt the term " cell." Every cell 

 originates by the subdivision of another cell, and the life 

 history of every living organism is but the story of how a 

 single cell, the fertilised ovule or the ovum, multiplies, and 

 how its descendants become differentiated into the various 

 tissues and organs of the adult. 



The early histologists soon noticed that each one of these 

 little living bricks which build up the body walls contains 

 in its interior a structure of more solid consistency than the 

 surrounding protoplasmic jelly in which it is embedded, and 

 the term "nucleus" was adopted as its name. The nucleus 

 is often difficult to see in cells which are examined in a fresh 

 unaltered condition, but treatment with a dilute acid or with 

 a dye will readily bring it into view, for the majority of 

 stains which are employed for microscopic purposes colour 

 the nucleus more deeply than the rest of the cell. 



As the microscope became a more perfect optical instru 

 ment, and as microscopic technique improved, and the list of 

 appropriate dyes grew longer, the structure of the nucleus 

 became clearer ; its investing membrane, its network of fibrils, 

 and nucleoli floating freely in the sap which occupied the 

 interstices of the network were recognised. Microscopists 

 introduced a number of names for the materials of which the 

 component parts of the nucleus were composed, although at 

 that time there was no knowledge of the chemistry of these 

 fantastically labelled substances. One of these terms has out- 

 lived the rest, namely the word " chromatin " or chromoplasm ; 



197 



