Complex sentence: In the late 19th-century and early 20th century, trends in xenotransplantation included the work of Charles-Édouard Brown-Séquard, who in 1889 injected himself under the skin with extracts from ground-up dog and guinea pig testicles.
Split into simpler sentences: In the late 19th-century and early 20th century, trends in xenotransplantation (transplanting tissue from one species to another) included the work of Charles-Édouard Brown-Séquard. In 1889, he injected himself under the skin with extracts from ground-up dog and guinea pig testicles.