suggestion is therefore put forth that ulcer disease may be regarded 

 as a clinical entity caused by any one or more of a nimber of different 

 organisms, rather than a disease consistently produced by a specific 

 organism. Furunculosis, on the other hand, is brought about by a 

 specific organism, B. salmonicida . 



The symptoms and pathology of ulcer disease also differ in 

 several respects from those of furunculosis (see below). However, if 

 B. salmonicida is found on occasion to produce lesions suggesting ulcer 

 disease, as has been reported (Davis 194-6), it would perhaps be better 

 to refer to the disease as furunculosis. IThen determining whether or 

 not ulcer disease is present, the symptoms and pathology would seem to 

 be the important aspect of the disease, the organism being of secondary 

 importance except vrhen B. salmonicida is present. In the case of 

 furunculosis, B. salmonicida must be present to produce this disease, 

 the sjTP.ptoms and pathology receiving som.ewhat less emphasis accordingly. 

 In differentiating between ulcer disease and furunculosis, these 

 distinctions would seem, logical in the light of our knoifledge at the 

 present time. 



Pathology 



The first recognizable symptoms of ulcer disease are raised, 

 somewhat tufted, v/hite spots consisting of fine shreds of superficial 

 skin layers which Fish (1935) named "epithelial tufts". These tufts 

 may appear on any part of the body, even on fins, but in m.ost cases the 

 first ones are found on the body proper. They are first noticed when 

 about 1 mm. in diameter and may be as much as 3 or 4- mm. across before 

 the coritim is penetrated and a recognizable ulcer is formed. A casual 

 inspection might lead to the conclusion that these tufts are small patches 

 of fungus (Wolf 1938). 



In 1934- Fish called attention to the fact that the pathology of 

 ulcer disease differs from furunculosis in several important points. 

 Borderline cases may be found, however, particularly in fingerling trout 

 which are exceedingly hard to diagnose accurately without resorting to 

 bacteriological examination. 



In the first place, with ulcer disease the lesions are clear-cut, 

 the whole picture being typical of a sloughing necrosis progressing from 

 the external surface imrard (Fish 1934-). According to Wolf (1938), 

 exposed muscle tissue often appears firm and healthy, but he states that 

 this is by no means constant^ as inflammation may extend for some 

 distance around the ulcer. 



Secondly, the contents of the lesions of ulcer disease are usually 

 light in color and easily washed away., leaving the gra^y'ish-white 

 muscular tissue (of trout) fully e^^Dosed (Davis 1946). Furunculosis is 

 an internal infection which moves towards the surface and produces 



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