38 NORMAL HISTOLOGY. 



which is a fibrous sponge-work containing a dense body, the centro- 

 some. The centrosphere multiplies by division, and thus initiates 

 the complicated processes by which one cell develops into two. 



(4) The nucleus. This is the larger, rounded, dense portion of 

 protoplasm. Its protoplasm is styled nucleoplasm. Its structure is 

 similar to that of the cytoplasm, consisting of an outer, dense ecto- 

 sarc and an inner sponge- work containing one or more nucleoli and 

 the chromatin, a substance very susceptible to stains. The nucleus 

 and centrospheres constitute the centers of vitality, the sources of 

 growth and vital phenomena. 



(5) The valcuole. This is the cell cavity and contains a watery 

 fluid or food masses for the nourishment of the cell. There may 

 be several vacuoles in a cell. In very young cells there is no vacuole, 

 the protoplasm filling the entire space. Old cells lose their proto- 

 plasm and may be empty or filled with the products of assimilation. 



With plant cells the cytoplasm often forms a layer within the 

 cell-wall, called the primordial-utricle. 



CELL CONTENTS. 



Besides the structures above named, the cell contains the chromat- 

 ophores, starch, mineral salts, proteids, fat, volatile oils, alkaloids, 

 ferments, and pigments. 



(1) The chromatophores are the color bearers. Among plants 

 there are three kinds the chloroplasts, leucoplasts, and chromo- 

 plasts. The chloroplasts contain the green coloring matter, called 

 chlorophyl. Some animals contain chlorophyl, as, for example, the 

 Green Euglaena. Chlorophyl has the power to decompose carbon- 

 di-oxide. Its chemical composition is unknown. It is soluble in 

 alcohol. The chromoplasts are the proteid products which contain 

 the coloring matter that gives the color to flowers and fruits. The 

 leucoplasts, or amyloplasts, are corpuscles which engage in the 

 manufacture of starch granules. They are found in portions of a 

 plant removed from light. 



(2) Starch, C 6 H 10 O 5 , is found in the cell and is produced 

 within the chloroplasts by the union of carbon (obtained from C0 2 ) 



and water. Reaction : 



C0 2 =C+20 



6C + 5ff 2 0=C 6 H 10 5 



