The physiologist John Scott Haldane focused his research on the mechanics of breathing, particularly in extreme conditions, such as in sewers, on mountain-tops and down mines (in which he was the first to introduce canaries to test for poisonous gases). He tested his theories by experimenting on himself. Haldane applied his findings to areas of public and industrial health. He developed a method whereby deep-sea divers could resurface and avoid decompression sickness or ‘the bends’. In this photograph Haldane poses in profile displaying his diving equipment. His diving experiments for the British Admiralty were carried out in top secret - the presence of the German soldier beside him is a mystery.