The Stolen Bacillus: and Other incidents

The Stolen Bacillus and Other Incidents is a collection of fifteen fantasy and science fiction short stories.
In the title story, the Bacteriologist has a visitor to his laboratory, a pale stranger who arrives with a letter of introduction from a good friend of the scientist. The scientist shows his visitor the cholera bacillus under a microscope and they talk about the disease. The visitor is particularly interested in a vial containing living bacteria, and the scientist describes the power of cholera, saying what a terrible epidemic could be caused if a tube such as the one he holds were to be opened into the water supply. As soon as the visitor has gone, the scientist realizes the vial of bacteria is missing,