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 
Fic. 1.— Diagram of o cell. as =attraction-sphere; c = centrosome; 
ch =chromatin reticulum; cr = chromidia; cc = ectoplasm; cn = cn- 
doplasm; / = karyosome; J = linin; m = mitochondria; me = mcta- 
plasm; nm=nuclear membrane; p= plastid; p/ = plasmosome or 
nucleolus; s = spongioplasm; » = 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 
