PROTOZOA 169 



although geese have been infected by inoculating them with the blood 

 of an infected chicken. The cliff-swallow [Petrochelidon albifrons) from 

 America is a bird with a strictly host-specific Plasmodium^ which, up to 

 date, has not been recorded from any other bird. 



These various species of bird Plasmodium, and in fact most of the 

 parasitic forms, can only be studied and identified after submitting 

 them to elaborate staining processes. Without the sharp contrasts 

 produced by artificial dyes the minute structural differences would 

 remain invisible to the human eye. A drop of blood from an infected 

 bird is spread thinly on a glass slide and then dried. Subsequently this 

 film is treated with certain dyes to which the various parts of the blood 

 cells and the parasite react in a particular manner. 



The different species of bird Plasmodium are separated on such 

 characters as the shape of the gametocyte, the number of merozoites in 

 one cell, the shape of the pigment granules and other similar types of 

 peculiarities. It is a matter of considerable difficulty and the accurate 

 identification of Plasmodium is unquestionably a matter for a highly 

 trained specialist. 



The allied genera of bird malaria parasites. We have already mentioned 

 that the unfortunate class Aves is afflicted by two allied genera of 

 Protozoa, to which man is luckily immune. One of these, Leucocytozoon 

 (Fig. 2,b), was found by Coles to be the commonest parasite in the blood 

 of British birds. It is recorded from a number of hosts including the 

 thrush, blackbird, jay, starfing, blue-tit, moorhen, pigeon, grouse, 

 tawny owl and brambling. Swallows are especially susceptible and 

 possibly acquire their heaviest infections if they gather in flocks in reed 

 beds prior to autumn migration — for, as nestlings, they are free of 

 infection. About 68 species of Leucocytozoon have been named, all of 

 which are confined to birds. In the United States it is sometimes the 

 cause of fatal epidemics among domestic ducks and turkeys. The 

 known insect-vectors are species of black-fly [Simuliidae) . 



The genus Haemoproteus (Fig. 2,c), which also parasitises reptiles, has 

 been found in the blood of various wild birds in Britain including the 

 chaffinch, thrush, blackbird, starling, wood-pigeon and grouse. About 

 45 species have been described and named from various countries, but 

 many of these are probably only new names for "old" species. Haemo- 

 proteus is widely distributed and very common — a fact which is readily 

 appreciated when it is realised that in the United States this parasite is 

 found in 50 to 60 per cent, of certain thrushes and in 80 per cent, of 



