30 



HUMAN PHYSIOLOGY. 



clearer and more fluent substance, the hyaloplasm. The relative 

 amount of these two constituents varies in different cells, the propor- 

 tion of hyaloplasm being usually greater in young cells. The arrange- 

 ment 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 protoplasm undergoes chemic 



Nuclear mem- 

 brane. 



Linin. 



Nuclear fluid 

 (matrix). 



Nucleolus. 



Chromatin "*' 

 cords (nuclear 

 network) . 



Nodal enlarge- '*' 

 ments of the 

 chromatin. 



Cell membrane. 



Spongioplasm. 

 Hyaloplasm. 



Foreign inclo- 

 sures. 



FIG. 2. DIAGRAM OF A CELL. 

 Microsomes and spongioplasm are only partly drawn. 



changes and is transformed into a thin, transparent, homogeneous 

 membrane, the cell membrane, which completely incloses the cell 

 substance. The cell membrane is permeable to water and watery 

 solutions of various inorganic and organic substances. It is, how- 

 ever, not an essential part of the cell. 



The nucleus is a small vesicular body embedded in the protoplasm 

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

 consists of a distinct membrane, composed of amphipyrenin, inclosing 

 the nuclear contents. The latter consists of a homogeneous amor- 

 phous substance, the nuclear matrix, in which is embedded the 

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



