India. Such an idea is countenanced by the fact that certain medical men practising in Africa, good observers, declare that black water fever is of comparatively recent introduction there; and, moreover, that it is yearly becoming more common in that continent. In certain States of the American Union it seems to have been only recently introduced; Meek says it first appeared in Texas in 1886.
Topographical distribution.— Although black water fever has a wide general distribution, it is limited in its endemicity to low, swampy grounds; and although, as reported by several authors, it sometimes occurs at high altitudes, this does not prove that infection took place there. We know that the disease may remain latent for a considerable time, that those who have been infected may have relapses at long intervals, and that the clinical manifestations may appear for the first time far from the place in which the infection was contracted. It is a common belief among the older residents in British Central Africa that a change of district, particularly from one level to another, causes blackwater fever, an opinion based on the experience that many cases occur soon after such a change. Amongst Europeans in British Central Africa such changes of district are frequent, and, as it is only a day's journey from the lowlands to the highlands, it is reasonable to infer that the majority of the cases which occur on the highlands depend on infection contracted previously in the swampy regions at the foot of mountains, and in the season during which the conditions favouring infection are most prevalent.
Seasonal prevalence.— In the Southern States of the American Union blackwater fever is reported to be especially frequent in late summer and in autumn. On the West Coast of Africa it seems to prevail at the close of the rainy season (August and September). For British Central Africa we have no definite information on this point. Like other infectious diseases, the acquisition of the germ cause of blackwater fever is directly or indirectly dependent on special meteorological conditions. The first clinical
