“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 improvise the bathroom as a dark-room and get everything ready so that we can start in bright and early.”

We were, indeed, up early.  One never has difficulty in getting up early in the country:  it is so noisy, at least to a city-bred man.  City noise at five A.M. is sepulchral silence compared with bucolic activity at that hour.

There were a dozen negatives which I set about developing after Craig had used up all our films.  Meanwhile, he busied himself adjusting his microscope and test-tubes and getting the agar slides ready for examination.

Shirt-sleeves rolled up, I was deeply immersed in my work when I heard a shout in the next room, and the bathroom door flew open.

“Confound you, Kennedy, do you want to ruin these films!” I cried.

He shut the door with a bang.  “Hurrah, Walter!” he exclaimed.  “I think I have it, at last.  I have just found some most promising colonies of the bacilli on one of my slides.”

I almost dropped the pan of acid I was holding, in my excitement.  “Well,” I said, concealing my own surprise, “I’ve found out something, too.  Every one of these finger-prints so far is from the same pair of hands.”

We scarcely ate any breakfast, and were soon on our way up to the hall.  Craig had provided himself at the local stationer’s with an inking-pad, such as is used for rubber stamps.  At the hall he proceeded to get the impressions of the fingers and thumbs of all the servants.

It was quite a long and difficult piece of work to compare the finger-prints we had taken with those photographed, in spite of the fact that writers descant on the ease with which criminals are traced by this system devised by the famous Galton.  However, we at last finished the job between us; or rather Craig finished it, with an occasional remark from me.  His dexterity amazed me; it was more than mere book knowledge.