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XIV] which are free from blackwater fever contract the disease just like Europeans when they come within its reach. Plehn mentions a serious outbreak of blackwater fever among the blacks in the Cameroons, the disease especially attacking those who had come to the coast from the interior. Reynolds says that the disease occurs sporadically amongst the natives of Ashanti. Among the circumstances which predispose to the active clinical manifestation of the blackwater-fever infection, debility from previous illness, bad food, or hardship have undoubtedly a powerful influence. It is usually in those who have suffered from subtertian infection, more rarely from tertian and quartan infections, or from dysentery, or who are "run down " from any cause, that blackwater fever appears, although cases of the disease in strong, healthy individuals of recent arrival have frequently occurred.

Length of residence.— It has been repeated again and again that Europeans are rarely attacked within the first year of residence in a blackwater-fever country, and great stress has been laid on this statement by those who believe that the hæmoglobinuria is not the special feature of a specific disease, but only a symptom of ordinary malaria in people who have previously suffered from several attacks of the prevailing intermittent fever. We know, however, that although in most cases attacks of the more widely spread subtertian may precede blackwater-fever infection, yet there are many cases on record in which blackwater fever occurred before any kind of "malaria" had manifested itself. Plehn, Scott, Ritchie, Cardamatis, Lynch, Hearsey, Daniels and others have reported cases of blackwater fever in robust individuals who were attacked within two or three months of their arrival in a blackwater-fever country. I have frequently been told by officers in the African colonial service that the attack of blackwater fever for which they were invalided suddenly developed while they appeared to be in perfect health and without any malarial antecedents. Daniels states that few cases occur during the first six months' residence, that they rapidly increase during the next six