THE PROTOPLASMIC SYSTEM 



forms like bacteria; the compounding of nuclei themselves 

 (a result easily obtained experimentally in normally mono- 

 nuclear cells) leads to the multi-nucleate, syncytial or 

 polyenergid condition. To a consideration of that proto- 

 plasmic system which is most widespread in occurrence and 

 which reveals itself as a simple membrane-enclosed cell 

 with a single nucleus, I now turn. 



For most organisms in both the animal and the plant 

 kingdom this cell is the basic structural unit, no matter 

 how complex or how large such an animal or plant may be. 

 A whale and a giant red-wood tree as well as minute forms 

 like a vinegar eel and a thread of green alga are patterns 

 of cells. Animals and plants also exist as single cells, 

 which within their boundary complete their life-cycles, 

 exhibiting the vital activities shown by the more complexly 

 organized individuals. These activities are perfect; diges- 

 tion, respiration, conduction, contraction, reproduction, in 

 a unicellular organism are as complete, though not so 

 complex, as in man. These individuals In their organiza- 

 tion and behavior reveal the single cell as an Independent 

 unit. At first one Is amazed that microscopic creatures like 

 the slipper-animalcule and the diatom, a plant of micro- 

 scopic size, can carry on the functions of more highly 

 organized forms of life; they seem at first to be imitations 

 of the latter. But observation teaches that the millions of 

 cells which make up the body of a multicellular animal or 

 plant have lost in capacity: no one cell In them can perform 

 all the functions to the same degree that a single-celled 

 Individual can carry out. 



This loss of capacity is compensated for by an emphasis 

 on some one function, as shown, for example, In cells In 

 the human body. In It some parts, which together make up 

 the nervous system, take over the business of conduction 

 which is developed to a high degree. Other parts, the 

 muscles, emphasize contraction; still others, respiration, 



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