Julius von Mayer. Engraving of Julius Robert von Mayer (1814-78), German physician and a pioneer of the theory of the conservation of energy. Mayer noted that the blood retained more oxygen in hot weather. He deduced that this was because the body required less oxygen to maintain body heat, and concluded that there was a fixed relationship be- tween heat and work. He studied the specific heat of gases, & argued that a gas cools as it expands because the heat is used up in expanding against atmospheric pressure. He later applied his theory of the conservation of energy more widely. He suffered from a nervous breakdown because he felt that his contemporaries largely ignored his work.