402 THE ETIOLOGY OF TROPICAL DISEASES 



inhabitants of the houses facing north were attacked much more 

 than others, and it was found that both these houses and the streets 

 in which they stood were distinguished by an exceptional degree of 

 humidity. 



In 1901 the United States Army Commission reported, after 

 extensive investigations into the etiology of yellow fever, that whilst 

 B. icter aides was not always present in cases of yellow fever, the 

 blood of the patient appeared to contain the virus, whatever it was, 

 and retained it after being passed through a Berkefeld filter. The 

 Commission further reported that the disease was not communicable 

 by direct contact with those suffering from the disease, but was 

 probably communicated by mosquitoes in a similar way to malaria. 

 The species of mosquito found capable of carrying the infection in 

 this way is the Stegomyia fasciata. Though the matter was not 

 proved, nor the nature of the virus determined, preventive mea- 

 sures were adopted in Havana on the mosquito hypothesis, with 

 the remarkable result that the disease was stamped out. 

 Gruit^ras of Havana has carried out further experiments which 

 confirm many of the Commission's findings, and, in particular, the 

 transmission of the disease by mosquitoes.* 



In 1902 a United States Army Expedition was appointed to 

 reinvestigate the subject, and it reported in 1903. The chief 

 conclusions reached were as follows : (1) Bacteriological examination 

 of the blood of persons with uncomplicated yellow fever during life, 

 as well as of organs and blood immediately after death, is negative. 

 (2) The mosquito known as Stegomyia fasciata, when allowed to suck 

 the blood of a yellow fever patient after the lapse of forty-one hours 

 after the onset of the disease, and subsequently fed on sugar and 

 water for twenty-two days can, if permitted to bite a non-immune 

 person, produce a severe attack of the disease. (3) Stegomyia fasciata, 

 contaminated by sucking the blood of a yellow fever patient, and 

 then killed, cut into sections and appropriately stained, presents with 

 regularity a protozoan parasite, Myxo-coccidium stegomyice, which 

 can be traced through a cycle of developments from the gamete to 

 the sporozoite. (4) Stegomyia fasciata, fed on the blood of a person 

 with malarial fever, on normal blood, or artificially, does not harbour 

 the myxo-coccidium. 



The etiology of yellow fever, therefore, remains at the present 

 time sub judice, but the probabilities are that the disease is mosquito- 

 borne and due not to bacteria but to sporozoal parasites. 



There are other tropical diseases to which brief reference must be made. 

 Malta Fever (Mediterranean fever) is common along the coast of the Mediter- 

 ranean and on its islands. It also occurs elsewhere. In 1886 Bruce cultivated from 



* American Medicine, 23rd November 1901, p. 809. 



