216 SECRETS OF ANIMAL LIFE 
remains an unread riddle; but, in spite of admittedly 
great difficulties, many evolutionists incline to the 
theory that very simple living creatures may have 
arisen from so-called inanimate materials as the 
outcome of natural synthetic processes. If this be 
so, a new significance appears in the abundance of 
carbon, hydrogen, and oxygen on the surface of the 
juvenile earth, and in what the chemists tell us of 
the unique ensemble of properties possessed by 
these three wonderful elements. They have great 
reactivity; they make great diversity possible; 
they make for concentrations and complexifica- 
tions, and these again favor the formation of 
colloidal systems. Now, all living creatures are 
essentially built up of proteins and other carbon 
compounds in a colloidal state. Only in that state 
could materialshave the pliancy and the per- 
meability which are characteristic of organisms, 
and that “energia’’ of which Thomas Graham 
wrote in 1861 that it “ may be looked upon as the 
probably primary source of the force appearing in 
the phenomena of vitality,” Now, while almost 
all substances can be made to assume the hetero- 
geneous colloidal state, with ultra-microscopic 
particles or droplets in suspension or dispersion in 
some medium, there is a notable readiness on the 
part of complex chemical substances to pass into 
that “dynamical state,” as Graham called it. But, 
as Professor Henderson reminds us, ‘of all the 
chemical elements, hydrogen, carbon, and oxygen 
possess the greatest number of compounds and 
