Pioneer in the field of hormone therapy, Charles-Edward Brown-Séquard (1817-1894) tried to stop the effects of aging on his contemporaries by injecting animal testicle extracts. His therapy was very popular in the last years of the 19th century. He even had followers in the following century, amongst whom Serge Voronoff (1866-1951), who grafted monkey testicles in replacement of human ones, or Paul Niehans (1882-1971) who practiced therapy using calf embryo cells in Switzerland.