THE DUCK HK'KNKSS IN UTAH. 9 



eyelid, or nictitating membrane, that lies concealed at the lower- 

 angle of the anterior corner of the eye. Id winking, this membrane 

 is drawn rapidly back across the eyeball to the posterior corner. In 

 birds with the duck sickness paralysis early affects the ttmscle (the 

 pyramidalis) controlling this third, eyelid, so that its ad ion 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 



