 In 1938, Lindbergh and Carrel described an [[artificial heart]] in the book in which they summarized their work, "The Culture of Organs", but it was decades before one was built.In later years, Lindbergh's pump was further developed by others, eventually leading to the construction of the first [[Cardiopulmonary bypass|heart-lung machine]].At the request of the United States military, Lindbergh traveled to Germany several times between 1936 and 1938 to evaluate German aviation.