touch any of the bottles on the outside. As for me, I wouldn't
have touched them for the world. In fact, I was getting so I
hesitated to touch anything. I was almost afraid to breathe,
though I knew there was no harm in that. However, it was not
danger of infection in touching the bottles that made Craig so
careful. He had noted, in the dim light of the station lamps,
what seemed to be finger-marks on the bottles, and they had
interested him, in fact, had decided him on a further
investigation of the bottles.

"I am now going to bring out these very faint finger-prints on
the bottles," remarked Craig, proceeding with his examination in
the better light of our room. "Here is some powder known to
chemists as 'grey powder'--mercury and chalk. I sprinkle it over
the faint markings, so, and then I brush it off with a
camel's-hair brush lightly. That brings out the imprint much more
clearly, as you can see. For instance, if you place your dry
thumb on a piece of white paper you leave no visible impression.
If grey powder is sprinkled over the spot and then brushed off a
distinct impression is seen. If the impression of the fingers is
left on something soft, like wax, it is often best to use
printers' ink to bring out the ridges and patterns of the
finger-marks. And so on for various materials. Quite a science
has been built up around finger-prints.

"I wish I had that enlarging camera which I have in my
laboratory. However, my ordinary camera will do, for all I want
is to preserve a record of these marks, and I can enlarge the
photographs later. In the morning I will photograph these marks
and you can do the developing of the films. To-night we'll