262 THE EVOLUTION OF LIFE 
conditions, to be quite as numerous, sometimes more 
numerous, than in those that have been exposed in 
the dark to the much higher temperature of the 
incubator. 
In all these solutions the supernatant fluid above 
the deposited silica remained perfectly clear. When 
the end of the tube had been cut off at a level 
sufficient to admit the passage of a wide-mouthed 
pipette, the latter (after sterilisation) was introduced 
into the tube, so as to remove some of the flakes of 
silica, and deposit them on a clean microscope slip 
for examination. 
In a flake taken from one of these tubes that had 
been exposed to light for five weeks, there is shown 
in Plate VI., Fig. 17, A, one of numerous small 
aggregates of Bacteria that were seen scattered 
through it. Around these aggregates were multi- 
tudes of solitary Bacteria and Micrococci, together 
with a comparatively small number of obviously 
inorganic particles or concretions. A few short 
chains closely resembling Streptococci were also 
seen. 
In Fig. 17, B, a portion of a large aggregate of 
Bacteria and Micrococci is shown (under a lower 
magnification) which, with others, was found in a 
similar tube except that it was composed of uviol 
glass. Solitary Bacteria, and also small groups of 
them, were scattered through the flakes, while the 
obvious inorganic concretions were very much more 
numerous than they were in the tube previously 
examined, though it had been prepared at the same 
time, and had been similarly exposed to light for five 
