INTRODUCTION 



5 



fibrillar phases, at different periods of growth and 

 in different conditions of physiological activity," 

 and that "apparently homogeneous protoplasm is a 

 complex mixture of substances which may assume 



FIG. 1. Diagram of a cell, as = attraction-sphere; c = centrosome; 

 ch = chromatin reticulum; cr = chromidia; ec ectoplasm; en = en- 

 doplasm; k = karyosome; Z = linin; m = mitochondria; me = meta- 

 plasm; nm nuclear membrane; p = plastid; pi = plasmosome or 

 nucleolus; s = spongioplasm; v = vacuole. 



various forms of visible structure according to its 

 modes of activity." 



The physical properties of protoplasm are not well 

 known, since most of our studies have been made with 

 fixed material. We know that protoplasm may 

 exist as a gel or a sol, and that it is intermediate 

 between true solids and true liquids, with many of 



