CELLS AND THEIR ASSOCIATION 39 



are which exceed this scale. The name protoplasm is 

 given to the characteristic material of which cells are 

 composed. In most cases there can be demonstrated 

 in a cell an internal mass which seems denser than the 

 rest. This is called the nucleus. When we recognize it 

 we at once have need of a word to describe the part of the 

 cell external to the nucleus; the word chosen is cytoplasm. 

 We are in the habit of speaking of the cell as a small mass 

 of living matter, but we are compelled to admit when 

 questioned that we do not know what proportion of the 

 whole is truly alive. This is a stimulating but rather 

 hopeless line of inquiry. 



When cells from different parts of the body are com- 

 pared we can recognize that some show special adapta- 



FIG. 1. To contrast the empty "cells" of a dry, woody tissue, en- 

 closed by substantial walls, with the "cells." of a soft, animal tissue 

 which are separate parcels of living matter. They are related to the 

 other somewhat as casts to their moulds. 



tion to particular uses while others are obviously of a 

 more primitive type. Cells that can be regarded as 

 primitive suggest to one that the standard form is the 

 sphere. Yet this form is seldom perfectly realized, 

 chiefly because cells which are pressed together naturally 

 come to have flattened surfaces at places of contact. 

 Thus they are like grapes that have been packed too 

 tightly. We ought to think of cells as of a very soft 

 consistency. The structural strength of the body as a 

 whole is gained through the development in it of deposits 

 and fibers which are not cellular but intercellular in nature. 



