FullReads

In our room we worked far into the night. Craig carefully swabbed out the bottom and sides of each bottle by inserting a little piece of cotton on the end of a long wire. Then he squeezed the water out of the cotton swab on small glass slides coated with agar-agar, or Japanese seaweed, a medium in which germ-cultures multiply rapidly. He put the slides away in a little oven with an alcohol-lamp which he had brought along, leaving them to remain overnight at blood heat.

I had noticed all this time that he was very particular not to 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 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.