IX] HISTORICAL I23 



Anopheles. [A. maculipennis and an Anopheles in which Ross 

 had already seen zygote stages of the malarial parasite in India.) 



Observations and experiments in Rome shewed that the 

 occurrence of Anopheline mosquitoes was especially charac- 

 teristic of malarious localities, and still more important that 

 patients contracted the disease when exposed to the bites of 

 Anopheles brought from notoriously malarious districts, or 

 those which had been previously fed on malarious subjects. 

 A final proof was the classical experiment of Manson, in which 

 Anopheles infected in Italy were allowed to feed upon two 

 volunteers in England, both of whom as a result contracted 

 malaria. 



This discovery, one of the most remarkable in the history 

 of medicine, was so opposed to popular ideas of the way in 

 which malaria was contracted, that for a time there were some 

 who doubted whether the simple explanation given by Ross's 

 experiments could explain all the facts regarding malaria 

 transmission. Especially the idea that malaria was supposed 

 to be contracted in remote and uninhabited swamps led to the 

 frequently expressed suggestion that there might be channels 

 of infection other than the mosquito, and a good deal was made 

 of certain bodies found by Ross within the parasitic cysts, and 

 called by him " black spores," as shewing that there might be 

 a cycle of development over and above that already known. 

 In order to explain the deadliness of tropical swamps and 

 jungles, others suggested that Anopheles obtained infection by 

 hereditary transmission from mosquito to mosquito, or from 

 the blood of bats or other wild animals. " Black spores," 

 however, are now known to be a species of Nosema attacking 

 the mosquito independently of malarial infection, whilst it is 

 now generally recognized that, contrary to current behef, 

 remote jungles and swamps in themselves are harmless, in the 

 absence of human inhabitants to yield infection. Neither 

 hereditary infection of mosquitoes nor their infection from wild 

 animals is now considered probable, and the view universally 

 held at the present time is that malaria is an infectious disease 

 passing from man to man, but requiring for this purpose the 

 presence of an intermediary transmitting host, the mosquito. 



