To one who, like the author, has the direct responsibility for the health, and so for the efficiency, of a large force of tropical labourers, the unavoidable isolation from fellow workers is a source of constant anxiety. Ever before him there is the fear that his views may become narrow and fixed from constantly seeing the same surroundings, and that his ideas would be altered had he more knowledge of what was happening in other places. The waste of only a single cent a coolie a day on a labour force of forty thousand means a direct loss of 126,000 Straits dollars (almost £15,000 sterling) per annum; and to increase the efficiency of the labour by a cent a day means a corresponding gain. Books and papers are valuable; but of more value still is a meeting with their authors, and an actual view of the field in which they work. Such thoughts and such fears have driven the writer to spend time and money in visiting other lands, so that he might benefit those under his care. In this book I have recorded what I saw and what I thought.

It includes a detailed account of the sanitary organization in Panama, the Mecca of the modern sanitarian. There he learns how one of the largest labour forces that the world has seen has been built up, and kept at a high degree of efficiency, in one of the deadliest climates in the tropics, when engaged on a great engineering work. My visit to British Guiana was made to determine the health conditions of another large labour force, also in the American tropics, when engaged in agricultural pursuits. But as a man, however careful he may be, can hardly help seeing through his own spectacles, I have begun with a chapter on sanitary work in the Malay States, and have there recorded some of the conclusions to which I have been led, and which seem to me to throw light on malaria in Italy, India, other parts of Asia, and the great Eastern Archipelago. My visit to Sumatra showed what excellent work is being done there to improve the health of large labour forces engaged in tropical agriculture.

Everywhere throughout the tropics great sanitary activity, and scientific investigation of disease, have followed Ross’ epoch-making discovery of the role played by the mosquito in the propagation of malaria. From India, from the Philippines, and from other countries, a series of invaluable reports are being issued, which will before long go far to make the tropics, if not a permanent home for the white races, at least a part of the world in which the white man may live with little more danger to health than in his own country. From the early chapters the reader will be able to gauge the views, and perhaps the bias and prejudices, of the author, when he set forth on his travels.