HISTOLOGY 



fatigue. It is evident, therefore, that the careful observation of proto- 

 plasmic granules is of very great importance. 



FIG. 3. 'FIBRILS IN A NERVE CELL. 



FIG. 4. VACUOLES IN A YOUNG 

 FAT CELL. 



Nucleus. 



Nucleolus. 

 f 



Capsule. Canaliculi. 

 FIG. 5. CANALS (TROPHOSPONG 

 IUM) IN A NERVE CELL. 



2. Fibrils. Protoplasm may be permeated 

 with a delicate meshwork of fibrils, which collec- 

 tively constitute the spongioplasm, or filar mass. 

 This is imbedded in the clear hyaloplasm, or 

 interfilar mass (Fig. i). In certain cells there are 

 filaments, known as mitochondria, which are 

 formed by the coalescence of rows of granules. 

 The relation between these structures and the 

 reagents used is discussed by Kingsbury (Anat. 

 Rec., 1912, vol. 6, pp. 39-52). The spongioplasm 

 may form an irregular network, or its constituent 

 fibrils may be parallel, passing from one end of 

 the cell to the other. In oblique and transverse 

 sections of such cells, the filaments are cut across, 

 so that they appear as short rods, or even as 

 granules. Fibrils may be extremely slender, as in 

 the case of those which radiate through the proto- 

 plasm at the time when the cell divides; or they 

 may be quite coarse, like the permanent fibrils 

 characteristic of certain muscle and nerve cells 



Reticular apparatus. 

 FIG.. 6. RETICULAR NETWORK (Fig. 3). 



3. Vacuoles. Protoplasm often contains large 

 or small drops of clear fluid, fat, or some other 

 substance less highly organized than the surround- 

 ing material (Fig. 4). In preserved cells the 

 spaces which were occupied by these droplets ap- 

 pear clear and empty, and are known as vacuoles. 



tiey vary greatly in size, and one or several of 

 them may be found in a single cell. 

 4. Canals. The protoplasm of certain cells is said to contain fine tubes 

 or clefts which communicate with lymphatic spaces outside of the cell 





