258 



MALARIA 



In birds, two parasites have become well known — 

 (i) the halteridium, (2) the proteosoma of Labbe. 

 Both have flagellated forms, and both are closely 

 allied to the plasmodium malariae. Using grey 

 mosquitoes and proteosoma-infected birds, Ross 

 showed by a large number of observations that it 

 was only from blood containing the proteosoma that 

 pigmented cells in the grey mosquito could be got ; 

 therefore that this cell is derived from the proteo- 

 soma, and is an evolutionary stage of that parasite. 

 Next, Ross proceeded to find out its exact location, 

 and found that it lay among the muscular fibres of 

 the wall of the mosquito's stomach. It grows large 

 (40-70 micromillimetres) and protrudes from the 

 external surface of the stomach, which under the 

 microscope appears as if covered with minute warts." 

 (Manson, at Edinburgh meeting of British Medical 

 Association, 1898.) 



These pigmented spherical cells give issue to 

 innumerable swarms of spindle-shaped bodies, 

 " germinal rods " ; and in infected mosquitoes Ross 

 has found these rods, in the glands that com- 

 municate with the proboscis. Thus the evidence 

 appeared complete, that the plasmodium malariae, 

 like many other parasites, had a special intermediate 

 host for its intermediate stage of development ; and 

 that this host was the dapple- winged mosquito. It 

 is impossible to over-estimate the infinite delicacy 

 and difficulty of Ross's work ; for instance, in his 

 " Abstract of Recent Experiments with Grey Mos- 

 quitoes,' he says that "out of 245 grey mosquitoes 

 fed on birds with proteosoma, 178, or 72 per cent., 

 contained pigmented cells ; out of 249 fed on blood 



