Illustration of a dog exposed to pneumonia with early abscess formation, dying five days after exposure to mustard gas. Mustard gas was used as a chemical warfare agent in the World War One. Exposure to mustard gas can cause coughing and shortness of breath in the short term. It also has long term effects such as mouth, throat and skin cancer as well as leukaemia. Illustration from Collected Studies on the Pathology of War Gas Poisoning, 1920.