PROTOPLASM. 



considered both as inert bodies and as the essential living basis of proto- 

 plasm. The simplest description of protoplasmic structure is that it 

 consists of a fluid ground substance in which microsomes are embedded. 



With high magnification it appears that the protoplasm contains a 

 network of filaments (called mitome, or the filar mass, from the Greek 

 (tiros and Latin filum, both meaning "a thread," spongioplasm is 

 another synonym). This network is embedded in a more or less homo- 

 geneous and chemically different ground substance (paramitome, interfilar 

 mass, or hyaloplasm). Some of the filaments appear as rows of micro- 

 somes, but small particles may also be found in the ground substance 

 between the filaments. The conception of protoplasm as fibrillar or 

 reticular has been considered at variance with the "granular theory," 

 yet undoubtedly both fibrils and granules occur in protoplasm. 



According to a third interpretation protoplasm has the structure of 

 foam, or of an emulsion, that is, it consists of minute droplets of one 

 substance completely surrounded by walls of a different substance. This 

 view, which has much in its favor, is not inconsistent with the presence 

 of granules or of fibrils scattered through the mass. 



In addition to these general char- 

 acteristics the protoplasm of particular 

 cells may contain other structures of 

 various significance. These may be 

 grouped as follows : 



i. Fibrils. Although an obscure 

 fibrillar network may be characteristic 

 of all cells, a high development and 

 orderly arrangement of fibrils occurs 

 only in certain specialized cells, as for 



example, in muscle, nerve, and connective tis- 

 sue cells. These fibrils are of very different 

 v / j*jff7 - sorts and will be described more fully in the 



\ / Jd&ZJLyL section on General Histology. 



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2. Granules. These are not the micro- 

 somes found in all protoplasm, but are larger 

 bodies of definite staining reaction, which often 

 are important secretory products elaborated by 

 the cell. In many gland cells, and in the 

 "granular" white blood corpuscles, these 

 structures are conspicuous. Other granules 

 may be excretory or waste products of the cell, 

 and some of these, which, without being 

 stained, are deeply colored, are called pigment granules. 



FIG. 2. FIBRILS IN A \ERVE CELL. 



Nissl's bodies. 



FIG. 3. CLUMPS OP GRANULES 

 (NissL's BODIES) IN A NERVE 

 CELL. 



