430 BULLETIN OF THE UXITED STATES FISH COMMISSION. 



stated to the commissioners tliat tbey liart observed sporadic cases of 

 the disease for years. We may add that we have recently nnderstood 

 from a lessee of fisheries on the North Esk that he had seen disease, 

 fi.sh, without recognizing tleni as diseased, for very many years; and 

 we have very little doubt that sporadic cases of the disease occur in 

 almost everj" river. 



The first symptom of this disease is the appearance of small grayish 

 or ashy discoloratiofis of the skiu, usually upon those parts of the body 

 which are devoid of scales, such as the top and sides of the head, the 

 delicate valvular membrane ou the inside of the jaws, the adipose fin, 

 and the soft skin at the bases of the other fins. Where such discoloured 

 patches occur on the scaly parts of the body the scales are hidden by a 

 film, and it might readily be supposed that they had been detached. 

 But if the discoloured film is gently washed or wiped off, the scales will 

 be found beneath perfectly undisturbed. On the scaleless part of the 

 body, also, the discoloured places often look as if they were the eifect of 

 bruises or abrasions, but careful examination of the skin fails to reveal 

 any evidence of external injury. 



The exact character of this affection of the skin may best be observed 

 in the recently formed isolated patches, not bigger than a sixpence, in 

 which the disease appears on the soft integument of the head. Such a 

 patch is usually nearly circular, and has a well defined margin separat- 

 ing it from the healthy skin. The central region of the patch is some- 

 what raised and more discolored than the rest, and faint ridges may 

 commonly be seen radiating from it, through the marginal zone, to the 

 edge of the patch. A single patch of this character may be observed 

 on a fresh-run fish, which, from its activity, the excellent condition of 

 its flesh, and the perfectly normal aspect of its internal organs, shows 

 itself otherwise to be in full health. 



When a patch of diseased skin has once apiteared, it rapidly increases 

 in size and runs into any other patches which may have ai)peared in its 

 neighborhood. The marginal zone, coustnntly extending into the 

 healthy surrounding skin, retains its previous characters, while the 

 ashy central part changes. It assumes the consistency of wet paper, 

 and can be detached in flakes, like a slough, from the skin which it 

 covers. If the subjacent surface is now examined it will be found that 

 the epidermis, or scarf-skin, has disappeared, and that the surface of the 

 vascular and sensitive derma, or true skin, beneath, is exposed. As the 

 diseased area extends, the papyraceous coat more and more completely 

 takes the place of the epidermis, until, in extremely bad cases, it may 

 invest the back and sides of a large salmon from snout to tail. 



The affection, liowever, is not confined to the epidermis. As the 

 patch acquires larger and larger dimensions, the derma, or true skin, in 

 its centre becomes subject to a process of ulceration; and thus a deep, 

 bleeding sore is formed, which eats down to the bones of the head and 

 sends oft" burrowing passages, or sinuses, from its margins. 



