3i6 EASTERN ETHIOPIA xxv 



kind are known as ha^niosporidia, and undergo an alter- 

 nation of generations corresponding with a change of 

 host. They are parasitic during the non-sexual cycle 

 in the l)lood of a verteljrate, and the sexual cycle is 

 passed in the gut of an invertebrate host. This change 

 of liost has been found to be effected in the case of the 

 malaria parasite l)y a particular species of mosquito 

 known as anopheles. That some species of culex was 

 the transmitting agent had been suspected by several 

 observers, especially by Laveran ; Ross, acting on these 

 suggestions, demonstrated that the malarial parasite in 

 the case of birds was transmitted by mosquitoes, and his 

 observations were soon amply confirmed by the Italian 

 workers Grassi, Bignami, and Bastianelli, in the case 

 of man. 



It is now accepted as a fact that the infectious agent 

 of malaria is introduced into the human organism by 

 the bite of an anopheles, which has itself been infected 

 by biting individuals whose blood contained the malarial 

 parasites. 



A very convincing series of experiments were carried 

 out, at the instigation of Manson, in which the in- 

 vestigators were the subjects. Drs. Sambon, Low, 

 Mr. Terzi, their servants and visitors, lived for the 

 three most malarial months of 1900 at Ostia, one of the 

 most malarial localities of the Roman Campagna. 

 They dwelt in huts, from which mosquitoes were ex- 

 cluded by a simple arrangement of wire gauze on the 

 doors and windows. They lived an ordinary out-of- 

 door life, took no quinine, Ijut were especially careful 

 to retire to their wire hut from sunset to sunrise. 

 Although their neighbours the Italian peasants were 

 each and all attacked ])y malaria, the dwellers in the 

 mosquito-proof huts enjoyed absolute immunity. 



The converse of this experiment was also carried out. 

 Mosquitoes fed iu Rome on persons suffering from 

 malaria were sent to London and were allowed to bite 

 two healthy men, Dr. P. Thurburn Manson and 



