30 



FUNDAMENTAL PRINCIPLES 



The nucleus, which is set off from the cytoplasm by a nuclear mem- 

 brane, shows a fine network of fibers known as Unin fibers ; and scattered 

 throughout the nucleus, adhering to these linin fibers, are masses of 

 another substance known as chromatin. This name was given to this 

 substance because it takes dyes or stains to a very high degree and when 

 the cell is subjected to these, the chromatin stands out as scattered, 

 deeply stained particles. A body which shows plainly in the nucleus is 

 known as a nucleolus. Nucleoli, however, are of various kinds. Some 

 are called plasmosomes or true nucleoli. Sometimes such a body is made 

 up of granules of the chromatin massed together and is called a karyosome 

 or chromatin nucleolus. The more fluid portion of the nucleoplasm 



Ce/J membrane 

 or wall 



Golgi 

 bodies 



Mefaplasm 



Plasma membrane 



Centra! body con- 

 taining two 

 cenfrioles 



Plasmosome 



Nucleus 



Cfiro matin 



Nuclear 

 sap 



Vacuole 



Nuclear 

 membrane 



Linin 



osome 



Kary> 



Cytoplasm 



Plastid 



Mitochondria 



Fig. 1 .- — Composite diagram of a cell having the form of a typical cell and containing 

 all the structures generally recognized as normal in cells not modified for any particular 

 function. 



between these structures which have been enumerated is often called 

 nuclear sap. 



In the cytoplasm appear several characteristic structures. A body 

 appears, under certain conditions, near the nucleus, known as the central 

 body, or centrosome, containing one or two granules called centrioles. 

 More or less soUd particles in the cell include living portions of the proto- 

 plasm which have some particular function to perform, such as the chloro- 

 phyll bodies which give the green color to plants. These have been given 

 the general term plastids. Included in plastids are mitochondria, or 

 chondriosomes, which are fiber-like and more compact structures, the 

 nature of which is in question ; and Golgi bodies, which may be scattered 

 through the cell or collected around the central body. Bits of food or 

 waste particles which have collectively been called metaplasm may be 

 present in the cytoplasm. Vacuoles are transparent droplets seen regu- 

 larly in certain cells or at certain times in other cells. 



