252 THE EVOLUTION OF LIFE 
was adopted rather than the use of flasks the 
necks of which were plugged with cotton-wool, 
because it permitted samples of the silica to be 
taken from time to time with a sterilised pipette, 
for examination, with rather less risk of contamina- 
tion than would have resulted from the withdrawal 
and replacement of plugs of cotton-wool. 
Reference will be made to a few of these experi- 
ments (which can be so easily repeated by others), 
because organisms undoubtedly occur in them rather 
more freely than they do in superheated and hermeti- 
cally sealed vessels ; and yet that this is not due to 
infection seems shown by the fact that just the same 
kind of organisms that are met with in the one case 
are also found in the other, as I shall subsequently 
show—the difference being that they are rather less 
abundant, and appear after a longer interval, where 
closed tubes and high temperature have been had 
recourse to. 
An interesting point not yet mentioned is, that 
the organisms found in these particular solutions 
containing silica, when heated to high or compara- 
tively low temperatures are, in part, organisms of a 
somewhat unusual character, of which I can find no 
description in bacteriological works. 
Results obtained with Saline Solutions which had 
previously been heated in Corked Flasks to 
100 C. for ten minutes. 
In Plate II., Fig. 5, A, a number of Bacteria, to- 
gether with two or three Torule, are seen, which 
