AN INTRODUCTION TO ZOOLOGY 



way, so that actually our knowledge of most of its details is obtained 

 from a study of the dead cell. One of the first objects of Cytology, 

 therefore, is to devise ways of killing the cell in such a manner that 

 its structure remains as much like the living cell as possible. This 

 process is termed fixation, and a number of different solutions have 

 been discovered for fixing cells and tissues. Each of these acts 

 most favourably with certain kinds of cells, or shows up certain 



FIG. 122. Diagram of a typical cell. From Kellicott. 



., aster c., centrosome (centriole) ; ch., chromatin ; cr., chromidia ; cs., centrosphere ; d., 

 deutoplasmic granules ; en., endoplasm ; ex., exoplasm (cortical plasm) ; hy., hyaloplasm ; k., 

 karyosome ; /., lining network ; m,, cell membrane ; n., nucleus ; nm., nuclear membrane ; 

 o., nucleolus ; p., plastids ; sp., spongioplasm ; v., fluid vacuoles (metaplasm). 



structures in the cell, or is specially adapted for use when it is to be 

 followed by certain staining substances ; and although some have 

 a much wider range of action than others, not one is the best for use 

 under all or any circumstances. It is beyond the scope of an 

 elementary book to go further into this important matter, but it 

 should be borne in mind that, in the description that follows, various 

 methods of treatment are necessary in order to render conspicuous 

 all the structures considered. 



