42 TEXT-BOOK OF PHYSIOLOGY. 



The relative amount of these two constituents varies in different 

 cells, the proportion of hyaloplasm being usually greater in young 

 cells. The arrangement of the fibers forming the spongioplasm also 

 varies, the fibers having sometimes a radial direction, in others a 

 concentric disposition, but most frequently being distributed evenly 

 in all directions. In many cells the outer portion of the cell proto- 

 plasm undergoes chemic changes and is transformed into a thin, 

 transparent, homogeneous membrane, the cell membrane, which 

 completely incloses the cell substance. The ceir membrane is 

 permeable to water and watery solutions of various inorganic and 

 organic substances. It is, however, not an essential part of the cell. 



The nucleus is a small vesicular body embedded in the proto- 

 plasm near the center of the cell. In the resting condition of the cell 



Nuclear membrane. v 



Linin. 



Nuclear fluid (matrix). 



Nucleolus. 



Chromatin-cords 

 (nuclear network). 



Nodal enlargements 

 of the chromatin. 



Cell membrane. 



-V Exoplasm. 



Microsomes. 

 Centrosoma. 



Spongioplasm. 

 Hyaloplasm. 

 Foreign inclosures. 



FIG. 2. DIAGRAM OF A CELL. Microsomes and spongioplasm are only partly drawn. 



it consists of a distinct membrane, composed of amphipyrenin, in- 

 closing the nuclear contents. The latter consists of a homogeneous 

 amorphous substance, the nuclear matrix, in which is embedded 

 the nuclear network. It can often be seen that a portion of one 

 side of the nucleus, called the pole, is free from this network. The 

 main cords of the network are arranged as V-shaped loops about it. 

 These main cords send out secondary branches or twigs, which, 

 uniting with one another, complete the network. The nuclear cords 

 are composed of granules of chromatin, so called because of its 

 affinity for certain staining materials, held together by an achromatin 

 substance known as linin. Besides the nuclear network, there are 

 embedded in the nuclear matrix one or more small bodies composed 



