THE DUCK SICKNESS IN UTAH. 9 
eyelid, or nictitating membrane, that lies concealed at the lower 
angle of the anterior corner of the eye. In winking, this membrane 
is drawn rapidly back across the eyeball to the posterior corner. In 
birds with the duck sickness paralysis early affects the muscle (the 
pyramidalis) controlling this third eyelid, so that its action is more or 
less weakened. Winking is very slow at first, then the nictitating 
membrane can come back only part way across the rounded eyeball. 
Gradually the action of the muscle lessens, until finally the third lid 
lies motionless in its normal position at the anterior canthus of the 
eye. To test the activity of this membrane it is necessary only to 
hold the bird's head firmly and then with some slender object, as a 
bit of grass stem, a toothpick, the handle of a scalpel, or a pair of 
tweezers, to touch gently the eyeball near the posterior corner and 
observe the action of the third lid. When this is unaffected it will 
spring back at once, perhaps several times, in an effort to protect 
the sensitive surface of the eyeball. In birds with the duck sickness 
it operates as has just been described. This one reaction serves as a 
ready means of distinguishing the duck sickness from any other dis- 
eased condition of waterfowl known to the writer. 
In connection with the symptom just described is another of inter- 
est. Lying within the orbit on the anterior surface of the eyeball is 
a large gland, known as the Harderian gland. This secretes a fluid 
that reaches the eyeball at its anterior corner below the nictitating 
membrane. In the duck sickness this gland always seems more or 
less affected and in most cases is considerably swollen, so much so, in 
fact, that the eyes are protuberant. Following this swelling the dis- 
charge of colorless, watery fluid from the gland becomes more copious. 
Normally it escapes at the anterior corner of the eye through two 
canals that unite and lead into the nasal chamber. In sick birds the 
secretion becomes greatly augmented, however, until these openings 
are not able to care for it, the eyes appear watery, and the fluid 
escapes between the lids. In some pintails kept under observation 
the escape of this fluid moistened the feathers of the entire side of the 
head. In a few hours this discharge becomes viscous and more or 
less opaque, and cements together the eyelids, while the augmenting 
supply held within puffs out the lids all around. The portion that 
escapes through the ducts passes through the inner nasal openings 
into the mouth. As the opening into the trachea (the glottis) lies 
immediately below, the fluid clogs it and interferes greatly with 
breathing. After two or three days the secretion becomes caked and 
cheeselike. When it thickens in large quantity it sometimes closes 
the trachea and causes strangulation. In a few cases the fluid pen- 
etrated to the bronchi, filling them completely and killing the bird. 
A severe irritation of the mucous membranes of the eye, including the 
nictitating membrane, is coupled with this discharge. In one case 
46651°— 18— Bull. 672 2 
