From A Labyrinth of Kingdoms: 10,000 Miles through Islamic Africa, by Steve Kemper (W. W. Norton, 2012), Kindle pp. 310-311:
On October 29 [Heinrich Barth] heard that a British expedition had steamed up the Benue River. He had urged this mission on the government two years earlier but hadn’t heard a word about it since. He traced the rumor to a man in Kano who had seen the steamer on the Benue. Barth questioned him closely and was convinced that the rumor was true.
Barth wouldn’t know the details for many months. The mission had left Britain in early June 1854. When its commander died soon after the boat reached the island of Fernando Po in the Gulf of Guinea, Dr. William Balfour Baikie assumed command. Baikie, who later became Barth’s friend and supporter, took the 100-foot steamer Pleiad up the Niger for 700 miles. In early August the Pleiad entered the Benue and ascended it for 250 miles. At the end of September Baikie turned around, reaching the Niger on October 20, while Barth was in Kano. By February 1855 the Pleiad was home.
Every previous excursion on the Niger had proven deadly to Europeans, mostly because of fever. But the Pleiad’s entire crew—twelve Europeans and fifty-four Africans—survived because of an experimental therapy—prophylactic doses of quinine. This success altered the course of African exploration. The voyage also proved Barth’s conviction that the heart of Africa could be opened to commerce through navigation of the Niger’s watershed.