HISTOLOGY. 



regard it as a permanent and essential part of a cell, which accordingly 

 consists of protoplasm, nucleus, and centrosome. 



PROTOPLASM. 



Protoplasm is the living substance of which cells are composed. 

 More specifically the term is applied to this living substance exclusive of 

 the nucleus, or to the corresponding dead material, provided that death 

 has not changed its physical properties. It has been proposed to substitute 

 the name cytoplasm for protoplasm in the restricted and earlier sense of 

 the term, to call the nuclear substance nucleoplasm [karyoplasm], and 

 to consider both cytoplasm and nucleoplasm as varieties of protoplasm. 

 Although these names are often employed, the cell substance apart from 

 the nucleus is ordinarily called protoplasm. 



Uiplosome in 



Centrosome. < ar ' choplasm . 



Interfilar mass. 



- -Xucleolus. 



'Microsomes. 



- -Cell membrane. 



FIG. i. DIAGRAM OF A CELL. Microsomes and filar mass only partly sketched. 



Protoplasm is a heterogeneous mixture of substances forming a soft, 

 viscid mass of neutral reaction. In distilled water it swells but does not 

 disappear. It consists of water, salts and organic substances, some in 

 solution, and some in a colloidal state. The organic bodies are classed as 

 proteids, glycogen or some allied carbohydrates, and lipoid (fat-like) 

 bodies. Protoplasm may exist in a numberless variety of forms. 



On microscopic examination protoplasm is seen to contain small 

 granules, microsomes. In different cells these vary in abundance and in 

 character. They may be absent from the outer layer of protoplasm, 

 the exoplasm, which is firmer and chemically different from the inner endo- 

 plasm, and perhaps has a separate function. The microsomes have been 



