Experiments with various gases, including those in the atmosphere such as oxygen and nitrogen, were made using animals as well as humans. The animal was placed, as here, in a Bell jar to which the experimental gas was added. This picture portrays the English doctor, Henry Hill Hickman (1800-1830), experimenting with carbon dioxide in an attempt to induce a state of suspended animation. He hoped to use the technique on patients undergoing surgery but was ridiculed by his colleagues, perhaps fortunately, since carbon dioxide gas may cause fatal suffocation. Watercolour and gouache by Richard Tennant Cooper.