THE CELL 89 



The entire substance surrounded by the cell wall is called proto- 

 plasm. This is a jelly-like or viscous material something like the white 

 of an egg. Probably most cells have a definite wall, though many animal 

 cells do not. On the inside of this cell wall there is a network, or reticu- 

 lum, in which are found little foreign bodies, plastids, and open spaces 

 called vacuoles. The network itself is called spongioplasm, because it 

 somewhat resembles a sponge. The liquid protoplasm on the inside of 

 this network is called hyaloplasm ( ). On the inside 



of the cell there is a seemingly smaller cell, called the nucleus. This 

 nucleus is considered the most important part of a cell. A cell may have 

 one nucleus, or it may have many. There is a nuclear wall just as there 

 is a cell wall, and on the inside of the nucleus there is also a network 

 or reticulum. 



When a cell has been chemically stained with various substances, 

 it is found that a portion of the network in the nucleus takes the stain, 

 while a portion does not, showing that this nuclear network is composed 

 of at least two different substances. The part which takes the stain is 

 called the chromatin ( ) network, and the part 



which does not take the stain is called linin ( ) 



network. This nuclear network taking the stain usually stands out quite 

 distinctly from the rest of the cell, making it appear at first glance as 

 though the entire nucleus had taken a great quantity of stain to itself. 



The substance lying within the network of the nucleus is called 

 nucleoplasm. It may happen that some cells do not have a definitely 

 outlined nucleus with a nuclear wall, but nevertheless these cells have 

 nuclear material scattered throughout the cell itself in the form of 

 granules; such granules are known as distributed nuclei. In the red 

 blood corpuscles of the human being there are no nuclei in the adult 

 form, although these cells are nucleated when they originally begin 

 growing. 



On the inside of the nucleus there is a smaller nucleus in turn which 

 is called the nucleolus ( ). 



At certain places in the nucleus where the various fibers of network 

 cross each other, there may be little knots, called net-knots, and these 

 must not be confused with the nucleoli. The chromatin itself appears in 

 a granular form, and the granules are called chromomeres ( ). 



There may even be two nucleoli in one nucleus. These stain quite 

 readily also, but appear somewhat different from the chromatin after 

 such staining. Exactly what the nucleolus does, biologists do not know. 

 It disappears during the time the cell divides and consequently has been 

 thought to be for the purpose of holding something in reserve for this 

 division process. 



All of the material within the cell walls but outside of the nucleus 

 is known as cytoplasm, to distinguish it from the nuclear material .within 

 the nuclear wall or membrane. 



