CHAPTEK II 



THE ANIMAL CELL 



AN animal cell is usually of microscopic dimensions, in the human 

 body varying from ^-J-^ to ^Vo f an i ncn ^ n diameter. 

 It consists of 



1. Protoplasm. This makes up the main substance of the cell. 



2. Nucleus: a vesicular body within the protoplasm, generally 

 situated near the centre of the cell. 



3. Centrosome and attraction sphere: these are contained within 

 the protoplasm, near the nucleus. 



These three portions demand separate study. 



Protoplasm. 



Protoplasm is a soft jelly-like material; it usually contains 

 minute particles or granules floating in it which are more solid in 

 consistency, or globules (vacuoles) containing a watery fluid may 

 be present. There is considerable difference 

 of opinion between histologists as to whether, 

 apart from this, protoplasm exhibits any 

 structure or is a homogeneous jelly. With 

 high powers of the microscope it can, how- 

 ever, be demonstrated that in many cells the 

 protoplasm can be differentiated into two 

 parts, a fine network of fibrillae in which 

 the more fluid and apparently structureless 

 portion of the protoplasm is contained. 

 This view of the structure of protoplasm is 

 shown diagrammatically in the accompanying 

 figure (fig. 5). 



This theory of protoplasmic structure 

 was advanced by Leydig, and has in more 

 recent years been adopted by Schafer, who 

 speaks of the network or spongework as the 

 reticulum or spongioplasm, and the more fluid portion in its 

 meshes as the enchylema or hyaloplasm. Biitschli, on the other 



FIG. 5. Diagram of an animal 

 cell consisting of fibrillated 

 protoplasm, containing a 

 nucleus. 



