18 Leucocytozoon Anatis 
The attitude of affected individuals varies considerably, depending 
upon the course of the disease. In some instances, ducks succumb 
during the first severe paroxysm, while in others exacerbations occur 
at intermittent periods without producing a fatal result. Affected 
ducks will lie in a semi-comatose condition with the neck bent backwards 
and the head resting upon the dorsal portion of the spinal column. 
When roused this condition of stupor gives way to a period of intense 
excitement, during which a series of remarkable evolutions are indulged 
in. The head occupies various positions, sometimes describing circles 
in the air, and at other periods, oscillating to and fro. In others the 
neck is completely turned upon itself with the head resting upon the 
ground in an upright position, as shown in PI. I, figs. 1 and 2. 
The power of equilibrium is also lost, the duck turning over back¬ 
wards until completely exhausted. In the majority of recovered birds, 
there also appears to be some difficulty in locomotion, a decided lame¬ 
ness being present in one or other of the legs, usually the left one. 
Another manifestation which is fairly constant, is a purulent ophthalmia, 
the eyes being completely closed with the lids adherent to each other. 
The mortality is exceptionally high, probably aggregating to 65- 
70 %, while the ducks which recover remain undersized and stunted 
(PI. I, fig. 3). 
Etiology. The causative agent is, as yet, undetermined, owing 
partly to the limited nature of our investigations. When first observed, 
the manifest cerebral disturbance was attributed by some poultrymen 
to the development of insect larvae in the nasal chambers through the 
deposition of eggs by a species of blue fly. In a few cases larvae were 
found in the frontal sinuses, but only in those instances in wlfich the 
affection was running a subacute course, the eggs probably being 
deposited after the duck was semi-comatose or moribund. In autopsies 
where the disease ran an acute course, larvae were never found. 
Microscopic examinations of the cerebro-spinal fluid, peritoneal 
exudates, etc., failed to reveal any organisms to which a pathogenic 
role could be ascribed, but as laboratory facilities were lacking at the 
time, cultural methods could not then be adopted, thus nullifying any 
general conclusion which might be drawn. 
An examination of the blood revealed a Leucocytozoon which was 
present in large numbers in the peripheral circulation of the affected 
ducks. 
Leucocytozoon anatis. This parasite, to which so far as we are aware, 
no previous reference has been made, was observed during the course 
