THE CELL IN GENERAL. 2$ 



according as the nucleus is in a state of activity or is 

 at rest. The nucleus may be very small in proportion 

 to the size of the cell-body, or may make up nearly 

 the entire bulk of the cell. In the processes of de- 

 generation and decomposition, and under the action 

 of certain chemical agents, the nucleus is more re- 

 sistent than the cell-body, and on treatment of the 

 cell with certain coloring agents, such as hsematoxy- 

 lin, the nucleus is more deeply stained than the cell- 

 body. Within the nucleus, again, we frequently 

 find one or more small spherical or irregular-shaped 

 bodies, looking like vesicles or shining granules, 

 which are called nucleoli. They would seem, in 

 some cases at least, to be connected with the above- 

 mentioned intranuclear network. Of the exact 

 nature and significance of the nucleolus, we have at 

 present little definite knowledge. 



Finally, a small proportion of animal cells are 

 enclosed by an envelope the cell-membrane, which 

 may be thick or thin, now presenting well-defined 

 structural peculiarities, and again quite homogeneous 

 and structureless. In many cases the cell-membrane 

 would seem to be simply a peripheral hardened 

 layer of the cell-body. 



It will thus be seen that we may have, in an animal 

 cell, four distinct structural elements : the body, the 

 nucleus, the nucleolus, and the membrane. It is only 

 in a few varieties of cells, however, that all of these 

 elements are present. The cell-membrane is the 



