THE TYPICAL CELL 5 



Nevertheless, distinct fibrils are often to be found in proto- 

 plasm, and frequently form an essential part of the cell structure. 

 In this list one finds the neurofibrils of nerve cells which Apathy 

 and Bethe have demonstrated to be frequently 

 continuous from one nerve cell to another ; the 

 longitudinal contractile fibrillae of muscle fibers ; 

 the intercellular bridge fibrils of epithelium, 

 which can often be traced through two or three 

 adjacent cells ; and finally the intracellular 

 " rod fibrils " of many epithelial cells. 



J IIG. 5. DEVELOPING 



Protoplasm frequently also contains spherical FAT CELLS . 

 vacuoles, which are formed by the accumulation The fat droplets, 

 of fluid droplets whose consistence differs from after extraction with 

 that of the surrounding protoplasm. These ^^ 

 droplets may be the result of metabolic activity Hematein and eosin. 

 within the protoplasm itself ; they are frequently x 55 - 

 of a fatty nature. 



Other products of cellular metabolism which appear within the 

 cell protoplasm are the secretory granules zymogen, mucinogen, 

 glycogen, etc. which are formed within the protoplasm of secret- 

 ing cells. 



The nucleus differs somewhat in structure from the surround- 

 ing cytoplasm. It contains a fluid nuclear matrix, or nuclear sap, 

 embedded in which are a chromatic and an achromatic nuclear 

 network. The achromatic reticulum is composed of very fine linin 

 threads, which form an exceedingly delicate mesh. 



The nuclear chromatin may or may not exist in the form of a 

 network. Its condition is very variable, and apparently is more 

 or less dependent upon the state of cellular activity as regards the 

 processes of reproduction. The chromatin may thus form a single 

 thread-like fibril of considerable length, which, under high mag- 

 nification, is seen to be composed of small discoid granules, the 

 chromomeres of Fol. 



During mitosis the chromatin thread is broken into a given 

 number of V-shaped segments or chromosome* ; the number of 

 these chromosomes varies in different animals, but is definite for 

 each species. In the resting stage, the phenomena of karyoki- 

 nesis having been completed, the daughter segments are capable 

 of reuniting to form a single thread, or, on the other hand, they 

 may disintegrate into still smaller granular particles. The gran- 

 ules thus formed are frequently scattered along the linin threads, 



