Three years later, Spencer Fullerton Baird called him to the Smithsonian Institution to work on its growing collection of North American reptiles, amphibians and fishes.

He worked at the museum for the next ten years and published numerous papers, many in collaboration with Baird.

[1] When the American Civil War broke out, he joined the Confederates as an agent for surgical and medical supplies.

During the Franco-Prussian War he served as a military physician and published an important paper on the typhoid fever after the siege of Paris.

[1] He retired in 1891 and spent the rest of his life in Neuilly-sur-Seine, where he died on 29 January 1895.