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246 THE EVOLUTION OF LIFE 
has just been sterilised by passing it four or five 
times through the flame of a spirit lamp, and the 
deposit is at once covered by a cover glass, which 
has been similarly treated. If organisms are found, 
they are generally photographed at once, or else 
after they have been stained by drawing a drop of 
a solution of eosin or of gentian violet beneath the 
cover glass. In case the specimen is reserved for 
future more careful examination, or with a view to 
see whether the organisms found will develop 
further, the cover glass is at once surrounded with 
some paraffin melting at about 105 I-.—which will 
sometimes prevent evaporation for several weeks, 
and allow Bacteria or Torule to multiply, or 
the latter to develop hyph, and thus remove any 
lingering doubt as to whether the organisms are 
or are not really living. 
Where the aperture of the tube is larger, the only . 
variation is that some of the deposit is withdrawn 
from the tube by a pipette, which has just been 
sterilised in the flame of the spirit lamp, and from it 
transferred to the sterilised microscope slip. 
With the solutions which I shall name presently, 
organisms will generally be found in the first one or 
two specimens taken from the tube, because I shall 
refer only to the solutions which have been found to 
be most productive. As I have said, the organisms 
will all be motionless, but their numbers, looking to 
the character of the fluids employed, will clearly 
testify to the fact that they must have developed 
within the tube after it had been heated—moreover, 
in the specimens mounted as I have described, the 
