THE VITAL PHENOMENA OF CELLS 3 



typical cell, is a small round or oval body contained within 

 the cell. It is usually surrounded by a distinct nuclear mem- 

 brane, except during division. Nuclei play an important role 

 in cell reproduction and cell nutrition. They are character- 

 ized by their affinity for certain stains, e. g. } hematoxylin. 



The substance of the nucleus, the karyoplasm, may be di- 

 vided into two parts the nuclear fibrils which form an ir- 

 regular reticulum, and the nuclear matrix which forms the 

 intervening semi-fluid mass. The nuclear fibrils, when prop- 

 erly stained, are found to consist of minute irregular masses 

 of a deeply colored substance, called chromatin, in recogni- 

 tion of their affinity for certain stains. The chromatin par- 

 ticles are supported within delicate and colorless threads of 

 linin. The nuclear matrix, which is semi-fluid in character 

 and which occupies the spaces between the nuclear fibrils, 

 possesses a very weak affinity for the stains used to color the 

 chromatin. Hence, it usually appears clear and untinted. 

 Chemically, the chromatin contains a substance nuclein, 

 which is rich in phosphorus. 



The nucleolus ordinarily appears as a small spherical mass 

 among the nuclear fibrils. It is supposed to be of little sig- 

 nificance in so far as the vital phenomena of the cell are con- 

 cerned. 



The Vital Phenomena of Cells. The vital phenomena of 

 the cell include all those processes and changes which it un- 

 dergoes during its life and which take place in the perform- 

 ance of its various functions. They include (i) metabolism, 

 (2) growth, (3) reproduction and (4) irritability. 



(i) Metabolism, includes all those processes by which the 

 cell is enabled to select from the various substances furnished 

 it and convert them into its own substance, and, secondly, 

 those processes whereby the cell is enabled to cast off the 

 waste products set free by its activity. The first process, that 

 by which the cell takes the simple substances furnished it and 

 converts them into its .complex compounds, is called anabol- 

 ism, or constructive metabolism. 



