On Wednesday 27 April 1898, Dr Luigi [Louis] Westenra Sambon (1865–1931) addressed the Royal Geographical Society in London on a topic of much interest to the Victorian public. An Anglo-French medical graduate of the University of Naples, a Fellow of the London Zoological Society and a recent visitor to Central Africa, he was well equipped to tackle the subject of the ‘Acclimatization of Europeans in Tropical Lands’. The ‘problem of tropical colonization’, he began, ‘is one of the most important and pressing with which European states have to deal. Civilization has favoured unlimited multiplication, and thereby intensified that struggle for existence the limitation of which seemed to be its very object…I know full well that the question of emigration is beset with a variety of moral, social, political, and economic difficulties; but it is the law of nature, and civilization has no better remedy for the evils caused by overcrowding.’

Even from these introductory remarks, it is already plain that Sambon's project was a compound product of medical diagnosis, colonial imperative, Darwinian demography and moral evaluation. And it is the rhetorical zone roughly marked out by this quadrilateral of disease, empire, struggle and virtue that I want to explore here. First, however, it will be instructive to return to that afternoon a century ago and spend a little more time listening in on the deliberations.