130 TROPICAL MEDICINE AND HYGIENE 



African native was not immune : Creole negroes usually 

 escaped. 



The series of outbreaks in Bermuda are of interest as 

 showing how in a place much visited epidemics were 

 frequent. Records of epidemics date from- 1699, followed 

 by others in 1779, 1796, 1812, 1818, 1819, 1837, 1843, 

 1853, 1856, and 1864. The mortality in these outbreaks 

 was usually comparatively low ; fatal cases occurred 

 amongst the blacks, but only in small proportion e.g., in 

 1864 there were only three deaths amongst 1,469 cases in 

 the coloured natives, 0*2 per cent., whilst 49 per thousand 

 of the white people attacked died. 



There can be little doubt that after an epidemic, and 

 probably before it, mild cases occur and keep the epidemic 

 alive. The epidemics in Bermuda of 1818 and 1819, 

 and again of 1837 and 1843, represent two epidemics 

 only. Whether the disease can remain restricted to cases 

 of the mild type, and the infection remain alive with no 

 manifestation of cases of the severer forms for periods of 

 ten, twenty, or fifty years, is a different question, and for 

 each country must be decided on the evidence in that 

 country and not on general principles. In the meantime, 

 even where the evidence that the disease is endemic is 

 fairly strong, quarantine regulations against places where 

 the disease exists in a virulent form should be enforced. 



Yellow fever is the most important member of a group 

 of diseases believed to be caused by protozoa, though the 

 parasites have not been found. The virus exists in the 

 blood plasma, is ultra microscopic, and the diseases are 

 carried by insects. A period elapses before the insect 

 which has imbibed the blood is capable of transmitting 

 the infection. Dengue fever is carried by Culex fatigans 

 and Stegomyia fasciata, and Phlebotomns fever is carried 

 by Phlebotomns papataci ; there are other known members 

 of this group. They are described in Part III. 



