30 



FUNDAMENTAL PRINCIPLES 



or chromatin nucleolus. The more fluid portion of the nucleoplasm 

 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 solid 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 



Plasma membrane 



Central body con 

 faining two 

 centrioles 



Plasmosome 



Nucleus 



Chromatin 



Nuclear 

 sap 



Vacuole 



Mefaplasm 



Cell wall 



Golgi 

 bodies 



Nuclear 

 membrane 



Linin 



Karyosome 

 Cytoplasm 



Plastid 

 Mitochondria 



Fig. 5. — Composite diagram of a cell having the form of a typical cell and containing 

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

 function. 



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. 



41. General Physiology of the Cell. — There is a division of labor 

 in the cell among the structures which have been named. The nucleus is, 

 in a sense, the vital center. Cytoplasm alone is unable to carry on its 

 activities and its life is brief after it is separated from the nucleus. Prob- 

 ably under the influence of substances formed by the nucleus and passed 

 out into the cytoplasm the latter does most of the ordinary work of the 

 cell, including the taking in of food, the carrying on of many of the chemi- 

 cal and physical changes associated with life, the passing out of waste, the 

 reception of all stimuli, and the movements which occur in response to 

 them. The chromatin is the medium by which hereditary characters are 



