situated between the dorsal and pelvic fins and in young trout is 

 probably the most characteristic symptom of the disease. Plehn (1911) 

 states that fish may become a general dull color, and on occasion even 

 blackish. Lethargy and quickening of breathing may also be present, 



Furunculosis is properly described as a general infection in 

 which focal lesions may or may not occur, according to the rapidity of 

 its progress (Furunculosis Committee 19.30). David (1926) claimed there 

 were six forms of the disease. The Furunculosis Committee (1935) 

 concluded that there were two main types of the disease; One which runs 

 a rapid courssj death occurring mth no external signs, and termed "ac-ut-e"; 

 the otherj termed "subacute/' is slower in its progress^, focal lesions 

 developing in the muscles of various parts of the bo(^. This is a 

 better classification. Nimerous variations from these two extremes do 

 occur^ including the carrier state (see below) which may last for a 

 considerable period of time. In general, the infection may last from 

 a few days to a few weeks or many months (Plehn 1911). 



Williamson (1928) and Davis (194-6) have emphasized the septicemic 

 nature of the disease., bacteria being carried to all parts of the body 

 in the blood stream. Often there is also focal destruction of the 

 dermis with disintegration of capillary vessels » The underlying muscle 

 is also involved in the destructive process,, which extends into the 

 connective tissue between muscle bundles. As described by Arkwright 

 (1912) there may be multiple abscess-like cavities under the skin^ 

 sometimes of large extent containing an opaque reddish liquid. These 

 cavities may be closed or open on the surface through small sinuses,, 

 and some may even penetrate into the body cavity (Furunculosis Committee 

 1930). Plehn (1911) has noted ulcers of the size and shape of a 

 needle, Arkwright (1912) found these subcutaneous and muscular lesions 

 most frequently along the lateral line,, but Davis (1946) states that 

 they ordinarily develop in the dorsal musclesj and sometimes have a 

 narked tendency to form at or near the base of the dorsal or pelvic fins. 



The kidney is frequently affected, and this organ may become 

 necrotic and semifluid (Furunculosis Committee 1930), Plehn (1911) four:d 

 that bacteria collected in the kidney in great numbers^ especially 

 in the glome.ruli where they could be seen on sectioning. 



The spleen may also be destroyed in the same way (Furunculosis 

 Committee 1930^ Duncan 1932). It is commonly enlarged and has a brigh"*-. 

 cheriy-red color (Davis 1946). If the spleen is crushed underneath a 

 co-^er slip (Davis 194-6) white clumps of bacteria can usually be sean^ 

 even where there are no other indications of disease. They may also be 

 -"5 9 en on sectioning. 



The liver is lighter in color than normally and has a tendency to 

 become fatty. Minute hemorrhages are often seen and in microscopic 

 preparations bacteria are found in and around blood vessels the walLs cf 

 irahlch have been damaged, Davis (1946) states that sectioning and staining 



32 



