Letter from Michael Heidelberger to C. W. Shilling, United States Department of the Navy

Heidelberger spent six weeks in India in early 1952 as a delegate to the Indian Science Congress, held in Calcutta. While there he seized the opportunity to study the immunological properties of elephants, an idea first proposed, half jokingly, by Oswald Avery when he had become frustrated with the small amounts of antiserum produced by rabbits, the standard experimental animal in immunology. Heidelberger injected human gamma globulin into the ear vein of a work elephant, and found that the animal was indeed a good producer of antiserum to the gamma globulin.