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 membrane, 

 except during division. Nuclei play an important role in cell 

 reproduction and cell nutrition. They are characterized by 

 their affinity for certain stains, e. g., hematoxylin. 



The substance of the nucleus, the karyoplasm, may be divided 

 into two parts the nuclear fibrils which form an irregular reticu- 

 lum, and the nuclear matrix which forms the intervening semi- 

 fluid mass. The nuclear fibrils, when properly stained, are 

 found to consist of minute irregular masses of a deeply colored 

 substance, called chromatin, in recognition of their affinity 

 for certain stains. The chromatin particles 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 con- 

 tains 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 signifi- 

 cance in so far as the vital phenomena of the cell are concerned. 



The Vital Phenomena of Cells. The vital phenomena of 

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

 goes during its life and which take place in the performance 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 proc- 

 esses 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 anabolism, or construc- 

 tive metabolism. 



