A. C. Coles 
48 
The Leucocytozoa of Birds. 
In ray experience Leucocytozoa are by far the commonest parasites 
found in the blood of birds. I have seen them in the thrush, blackbird, 
jay, pigeon, starling, moorhen and many others ; in fact I should expect 
to find them in almost any of the common birds, at any time of the 
year, often however in small numbers. 
In the blood of the blackbird and thrush, especially in young birds, 
I have met with an enormous infection, more than 20 leucocytozoa 
being seen in the field of ^ objective with a low ocular, in fact at the first 
glance at the preparation with a lower power one might think we were 
dealing with a case of leukaemia. In the birds I have examined, only 
the round or spherical forms were met with. I have never yet seen the 
spindle-shaped leucocytozoon. It may be argued that the forms I have 
met with have been the spindle-shaped specimens which have become 
rounded off after the blood was taken from the body. I am convinced 
that this has not been the case (except perhaps in a few cases in which 
the bird had been dead some time) as films were made and fixed at 
once by osmic acid vapour, or a fresh drop of blood was covered with 
a coverglass and examined immediately, and in no case has there been 
any approach to the appearance of a spindle-shaped body. That I 
.should not have met with the .spindle-shaped form is the more 
remarkable as I detected and made drawings of leucocytozoa as far 
back as 1904, but I then had no idea of their nature. (Plate III, 
figs. 27, 30 to 44.) 
Generally speaking the blood of a bird which contains these parasites 
shows only one stage of the leucocytozoa, usually the adult, at one time, 
and it is not common, except in the case of very young birds, to meet 
with all stages from the youngest to the fully grown parasite. 
It is difficult to dogmatise as to the nature of the host cell, 
generally it seems to be a leucocyte or an immature red cell. I am 
not convinced that leucocytozoa never contain pigment. 
It is common to find two or three young parasites in one host, and 
I have seen, in the blood of a young blackbird which had a very severe 
infection, five small round or oval parasites in one immature cell. In 
the adult stage two parasites, of the same or opposite sex, may not 
infrequently inhabit the same cell. 
The adult female Leucocytozoon shows a compact deeply stained 
nucleus in or near which is seen a granule which stains more deeply 
with Giemsa. In the adult male the nucleus is large, oval, and diffuse. 
