638 THE BOOK OF THE Doc. 



This is a common cause of deafness, and quacks pretend to cure it by pouring stuff 

 into the ear ; the qualified surgeon, on the other hand, directs his attention to the tube itself, 

 up which he passes a catheter, and thus restores communication with the drum, and consequently 

 hearing. 



The internal or real ear is composed of several curiously-shaped cavities, all communicating 

 one with the other. The first of these is called the vestibule. This vestibule has a window 

 (fenestra ovalis) opening into the drum. To the membrane covering this window is attached the 

 inner end of the delicate chain of bones already mentioned. From the vestibule on one side go 

 three semi-lunar canals, and on the other a curious-shaped cavity called the cochlea, the 

 opening through which the auditory nerve descends. Now, the whole of the cavities of the 

 internal ear are lined by a delicate membrane, and in this lining the auditory nerve ramifies and 

 is spread out, and the cavities of this internal ear are all filled with fluid. 



The physiology of hearing is simple enough. Sound, which is air in motion, passes down 

 the meatus or external passage, and sets the drum to vibrate ; the drum cannot vibrate without 

 pulling the little chain of bones inside it, this being attached to the other membrane, which closes 

 the aperture to the internal ear. This membrane likewise vibrates, and the motion is communicated 

 to the water in the cavities, and thus, of course, to the nerves, which carry the sensation to the 

 brain, and the brain takes cognizance thereof, and, being the thinking portion of the human 

 frame, or the frame of a dog either, it the brain knows well from experience what the sound 

 is, whether the report of a gun, the crack of a keeper's whip, or the whirring wings of a rising 

 covey. 



And now we get to the diseases of the ear ; and we may premise that although these are 

 apt to attack any portion of the organ of hearing, those of the external auditory canal are by 

 far and away the most numerous, and next in point of frequency come diseases of the flap of 

 the ear. 



Like skin diseases, diseases of the ear constitute a large proportion of the canine practitioner's 

 work. They are too often troublesome to heal, and not only that, but they are apt to recur. 



I. Chronic tit is. 



Chronic otitis, called also chronic inflammation of the ear, or more commonly canker. 



The term canker is rather objectionable, in that it tends to mislead the ignorant. As the 

 word sounds so like cancer, the disease is often considered to be of a cancerous nature ; and 

 being deemed incurable, no notice at all is taken of it. The word canker really means an 

 eating ulcer; and probably the word originated from that sort of disease we see on some 

 esculent roots, as turnips, carrots, &c., caused by larval worms. 



The word being so common, however, we are obliged to retain it. 



Chronic otitis, or canker, really is an inflammation of the lining or secreting membrane of 

 the external auditory canal, often extending to the outer surface of the tympanum itself. 



Causes. These are often very obscure ; and considerable difference of opinion exists among 

 authors on the subject. Youatt tells us that all water-dogs are subject to this disease. Mayhew 

 seems to doubt this, and instances the case of a number of water-dogs that were kept for the 

 purpose of retrieving wild fowl at the mouth of the Ex, none of which, although constantly 

 in the water, ever suffered from canker. 



But Youatt says, " When the whole body, except the head and ears, is surrounded by cold 

 water, there will be an unusual determination of blood to those parts, and, consequently, dis- 

 tension of the vessels, and a predisposition to inflammation." At first blush this seems logical 



