The present condition of uncertainty regarding the etiology of hemoglobinuric fever may well be likened to that regarding the etiology of kala-azar ten years ago, and the history in this respect of the latter disease is of peculiar interest to the students of hemoglobinuric fever, because it furnishes an excellent example of how preconceived opinions influence the work of careful observers, and illustrates the fallibility of deductions regarding the etiology of any disease when influenced by such opinions.
For many years kala-azar was regarded as a persistent form of malarial infection, or a form of malarial cachexia. As late as 1896 Leonard Rogers considered it to be a fatal form of malaria, while Ronald Ross, in 1898, stated it as his belief that it was a form of malarial fever complicated by some secondary infection. Giles, after careful study, had come to the conclusion that kala-azar was due