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 

 reticulum, in which are found little foreign bodies, plastids, and open 

 spaces called vacuoles. The network itself is called spongioplasm, be- 

 cause 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 the 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 the linin ( ) 



network. This nuclear network which takes 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 such red cells are nucleated when they originally begin 

 growing. 



On the inside of the nucleus there is in turn a smaller nucleus 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, but these 

 must not be confused with the nucleoli. The chromatin itself ap- 

 pears 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 serve the purpose of holding something in reserve for the 

 division process. 



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



