3i6 
EASTERN ETHIOPIA 
XXV 
kind are known as hsemosporidia. and undergo an alter¬ 
nation of generations corresponding with a change of 
host. They are parasitic during the non-sexual cycle 
in the blood of a vertebrate, and the sexual cycle is 
passed in the gut of an invertebrate host. This change 
of host has been found to be effected in the case of the 
malaria parasite by 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 
tlie bite of an anopheles, which has itself been infected 
by biting individuals whose blood contained the malarial 
parasites. 
A very convincing serie§ 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, but were especially careful 
to retire to their wire hut from sunset to sunrise. 
Although their neighbours the Italian peasants were 
each and all attacked by malaria, the dwellers in the 
mosquito-proof huts enjoyed absolute immunity. ' 
The converse of this experiment was also carried out. 
Mosquitoes fed in Rome on persons suffering from 
malaria were sent to London and were allowed to bite 
two healthy men. Dr. P. Thurburn Manson and 
