Joseph Barcroft, in 1917, tested hydrogen cyanide on himself as part of research into poison gas in World War I. He was shut in a chamber with a dog and exposed to the gas. Barcroft continued with the experiment even after the dog went into tetanic convulsions and appeared to die. The experiment was continued for less than two minutes. The next morning the dog was found to be alive and apparently fully recovered. It is not known why dogs are more susceptible to the gas than humans.