278 THE EVOLUTION OF LIFE 
some of the hottest stars, can take its place, wholly 
or in part, as one of the constituents of protoplasm.! 
I do not pretend that my experiments afford any 
distinct proof that such a substitution is possible— 
since carbon may have been present in the solutions, 
in the way of some accidental impurity, either in the 
distilled water or in the chemicals employed. 
Still, the experiments recorded in this and in the 
last chapter are very suggestive that such a sub- 
stitution may be possible, when we bear in mind 
(2) the freedom with which Moulds will grow in 
and on the surface of colloidal silica, as ‘originally 
observed by Roberts and Slack, and subsequently 
by myself; and when (4) we recognise that minute 
Moulds and other Micro-organisms will appear within 
closed tubes containing the solutions in question, 
though these have previously been exposed to high 
temperatures. It may be said that in such cases 
the organisms, if from no other source, have been 
capable of taking their carbon from the CO, of the 
air within the tube; but against this supposition, 
in the case of the sealed tubes, there is the fact 
(c) that the organisms are invariably found away 
from the air, in or upon the flakes of silica which 
collect at the bottom of the tube; and that for 
month after month they are to be found there only, 
' According to Ostwald (‘ Inorganic Chemistry,” translation, 1904, 
p. 425), ‘‘ The largest part of the earth’s surface is composed of silicon 
dioxide, or of its compounds: over a quarter of the solid crust of the 
earth is formed by silicon.” And in regard to the silicates of the 
alkali metals, which go by the name of waver glass, he says (p. 427): 
‘These salts are readily obtained by fusing quartz with the hydroxides 
or carbonates of the alkali metals.” 

