8 BULLETIN" 672, U. S. DEPARTMENT OF AGRICULTURE. 
these lower extremities become affected almost at once, and the 
bird sits on the full length of the tarsus instead of standing on the 
toes. These birds are unable to escape -when approached, but strug- 
gle with beating wings to rise to a standing position. In a short 
time they sink on the breast in the mud and then are entirely helpless. 
In ducks and most other species, except the shorebirds just men- 
tioned, the legs become affected more gradually. Individual ducks 
are able to swim for some time after they are unable to support the 
body in a standing position. Slowly the muscles become more 
helpless until, capable of slight movement only, the feet remain in 
normal position under the abdomen. Sick birds seem to sense this 
increasing helplessness, and, when able, endeavor to work their way 
out of the water on mud bars, or seek shelter, if available, in rushes 
or other aquatic growth. 
In the next stage of the sickness the neck muscles weaken and 
the head is supported with difficulty (PL II, fig. 1). Birds remain 
quiet unless frightened, and when disturbed the head, with slight 
control, sways drunkenly from side to side. Finally the bud lies, 
unable to move, with the head prone on one side (PI. Ill, fig. 1). 
At this point, if the individual is in water, death comes by drowning, 
but on land the bird may live for some time longer. Many, however, 
avert drowning by throwing the head on the back, where it lies in 
an unnatural position. 
Affected individuals early show considerable difficulty in breathing, 
and as the trouble progresses this is more acute. Inspiration be- 
comes increasingly difficult and may be spasmodic, while the number 
of respirations per minute is lessened. In a great majority of cases 
death comes from cessation of breathing due to paralysis of the 
muscles controlling this function. In some birds the muscles slowly 
become passive, until finally only those in the anterior thoracic 
region respond. The intake and outflow of air is slight, and on 
casual observation such birds might be considered dead. 
In severe cases the heart also is affected. Normally the pulse in 
a wild duck at rest and not unduly excited averages 120 beats per 
minute. With any struggling or attempt at flight it jumps at once 
to 180 or 200. In some severe cases of the duck sickness the heart 
action was weak and irregular. One mallard lived in the laboratory 
for two days with the heart beating only 30 times each minute and 
the respirations reduced to 8 for the same period. The body tem- 
perature (rectal) in sick birds remains about normal unless the heart 
is affected. \Yith a decrease in the circulation the temperature 
falls slowly from the normal register of 104° F. to 109.8° F. (mean, 
106.7°) to less than 100° F. 
One important external symptom, easily overlooked, remains to be 
mentioned. Besides upper and lower eyelids birds possess a third 
