32 BIOLOGY 



two, and frequently three, distinct substances are discernible 

 in it. 



1. A mesh work (reticulum) resembling fibers. 



2. A liquid (cytoplasm) occupying the meshes of the net- 

 work. 



3. Minute bodies (microsomata) (Gr. micros = small + 

 soma = body) scattered along the branches of the network, 

 regularly or irregularly, and frequently moving to and fro in the 

 cell. 



Activity of Protoplasm. If living protoplasm be studied under 

 the microscope, it will frequently show a type of motion called 

 streaming. This is due to minute granules constantly circu- 

 lating in a more or less definite or indefinite fashion within 

 the cell. Whether all protoplasm will show such motion we do 

 not know, but apparently whenever this substance is actually 

 alive this motion is present. Possibly this may not be true of 

 protoplasm that is known as dormant, but it is almost certainly 

 true of all active cells. 



THE NUCLEUS 



Lying within the cell substance there is a smaller body, 

 usually of an approximately spherical shape, called the nucleus 

 (Lat. nucleus = nut); Fig. 9n. This is a structure of extreme 

 complexity. It is, as a rule, bounded by a delicate nuclear mem- 

 brane nm, which holds the contents and separates them from 

 the surrounding cell substance. Within this membrane may be 

 found a jelly-like mass, very similar to, if not identical with, the 

 cell substance outside, and also included under the term pro- 

 toplasm. To distinguish these two parts of the protoplasm, 

 that inside of the nucleus is called karyoplasm (Gr. karyon = 

 nut + plasma = substance) or nucleoplasm, while that outside 

 is called cytoplasm (Gr. cytos = cell + plasma) ; Fig. 9 ky and cy. 

 In addition to karyoplasm, however, there are other distinct 

 parts in the nucleus. Delicate fibers run through it called linin 

 fibers (Fig. 90, and a small rounded body known as the nucle- 



