OTITIS EXTERNA— OTORRHEA 491 



cases both ears are involved. Middle aged or older animals 

 are affected most commonly. 



Etiology.— There are a variety of things having to do with 

 the cause of this condition: (a) Accumulations of cerumen 

 and dirt are common causative factors. These substances 

 cause irritation to the skin resulting in inflammation and 

 pyogenic infection. Animals with long pendent ears tend to 

 retain these materials and decomposition and infection are 

 thus formed, (b) Retention of debris from acute attacks 

 leads to further irritation and often produces a chronic form 

 of the disease with considerable thickening of the tissues, 

 (c) In young animals the condition is frequently associated 

 with distemper. Secondary infection during the progress 

 of the disease involves the auditory canal, (d) Occasionally 

 in dogs, but more commonly in rabbits, invasion with the 

 parasite Otodectes cynotis occurs. In this case the entire 

 canal is involved, even the internal ear. The parasites pro- 

 duce extensive irritation and an aggravated form of the dis- 

 ease, (e) May result from ulceration of the concha and 

 hematoma by extension of the process from continued 

 irritation. 



Symptoms.— In the early stages and when the condition 

 is acute the animal shows restlessness, shakes and scratches 

 its head and ears with its paws almost continuously, and 

 rubs them against objects. Along the margins of the ear is 

 often noticed a blood-mixed discharge. Direct examination 

 reveals the ear to be hot, sensitive and the surface covered 

 with a thick waxy secretion. Owing to the swelling of the 

 skin and contiguous tissues an ear speculum is often neces- 

 sary in order to examine thoroughly the lower portion of the 

 canal. During the later stages ulceration takes place and 

 more or less extensive pus formation is found. Palpating 

 the base of the concha and exerting some pressure a thick, 

 dark colored discharge will be forced out. The head is 

 usually held in a fixed position, and if one side only is affected 

 it will be held to that side. The condition may produce tem- 

 porary or permanent deafness. In rabbits, when due to 

 parasites, nervous symptoms are very common. This has 

 been observed in dogs. 



