INSECTS AND HUMAN DISEASE 111 



and by that means alone. In connection with the mosquito- 

 borne diseases, it is interesting to note that, although 

 filariasis was first actually proved to be transmitted by 

 these insects, more than one observer, at a far earlier date, 

 had a shrewd suspicion that yellow fever was likewise 

 transmitted. Surgeon-General Blair hinted as much, and 

 Dr Beauperthuy, in 1853, actually accused Stegomyia of 

 being the carrier ; and so far he was right, though his belief 

 that the insect obtained its poison from the soil was, as we 

 shall see presently, far from correct. 



Yellow fever is probably one of the oldest diseases of 

 mankind; it was known to the Aztecs, and Humboldt 

 mentions its occurrence in the eleventh century. It caused 

 enormous mortality among the followers of Christopher 

 Columbus; it decimated the Mexicans in the sixteenth 

 century, and the inhabitants of Martinique at a later date. 

 Originating probably in Brazil, the disease has spread 

 along trade routes to Central America, the Southern United 

 States, and the West Coast of Africa. It was not till 1881 

 that Dr Finlay enunciated the theory that the disease 

 was carried from man to man by Stegomyia', and about 

 that time a host of observers took the field ; many of them 

 succumbed to the disease they had come to study, and 

 although they were unable to actually find the parasite 

 causing yellow fever, they proved that neither the persons, 

 clothing, nor excretions of patients suffering from the 

 disease are infective. They proved, too, that a patient's 

 blood only contained the virus five days after infection, 

 and that then, if bitten by the mosquito Stegomyia fasciata, 

 and by this species alone, the insect would, after a lapse 

 of .time, itself become infective and capable of transmitting 

 the disease. These discoveries " swept away as if by magic 

 the traditional views, which filled very many volumes, as to 

 the nature, origin, and prevention of yellow jack." The 

 disease had been attributed to " droughts and to floods, to 

 the pestilential ' mangrove swamp,' to high temperatures, to 



