32 
Blood Parcoiites 
two specimens sent from Reading they were detected. Films were 
made from the peripheral and heart blood, lung, liver, spleen, and 
bone marrow. Parasites were found in the peripheral and heart blood 
and in smears from the lung and liver. They were never very frequent, 
but were more numerous in the lung, and were not detected in bone 
marrow. 
Tlie parasites are generally slightly curved, oval or sausage-shaped 
bodies with rounded ends, situated almost entirely in the mononuclear 
leucocytes. (Plate II, fig. 17.) 
They measure on an average 9 to 10 /u. in length and 3 to 4 /a in 
width. The protoplasm stains a reddish-blue colour and is slightly 
granular. 
The nucleus, generally round or oblong in shape, is composed of 
a compact mass of chromatin and it is situated in the centre, or more 
generally, somewhat nearer one end of the parasite. It measures about 
4’5 ya long and 2’75ya in width. The breadth of the nucleus is not 
infrequently equal to that of the parasite, but sometimes the latter is 
much naiTovver. 
This haemogregarine produces a marked karyolytic action on the 
nucleus of its host. It is rare to see a perfectly intact mononuclear 
leucocyte enclosing a parasite ; for the most part the latter has invaded 
and split up the nucleus and the protoplasm evidently has become 
decolourised and finally invisible, and this condition prevails in good 
films in which the surrounding leucocytes are perfect. Very often the 
parasite lies between portions of the nucleus, and the outline of the 
leucocyte is quite lost. Sometimes the nucleus of the host completely 
surrounds and encloses the haemogregarine. 
A few free haemogregarines were found, most frequently in the 
lung or heart blood, and these differ but slightly from the intra- 
leucocytic forms except that they may be a little narrower. The 
enclosed parasite is usually surrounded by a narrow unstained area, as 
if it were lying in a capsule. 
Very numerous films of the blood and organs of both field voles were 
carefully examined for multiplication cysts, but in only one such smear, 
that made from the lung, was a cyst found. (Plate II, fig. 15.) This 
was oval in shape, measured 20/r by 16 ya, and was surrounded by a 
narrow unstained halo. It stains a distinct blue colour with Giemsa, and 
contains a number of merozoites but these were evidently degenerated 
as their number, outline, or nucleus, could not be determined. The 
centre of the cyst consisted of granular debris also stained blue. Only 
