marked infiltration of leucocytes is then noticeable in the tissues 

 surrounding lesions. This leucocytic response definitely differentiates 

 ulcer disease from lurunculosis in which there is no such outstanding 

 infiltration. 



The heavy subcutaneous tissue band forming the corium of the 

 skin apparently offers very little resistance to the bacteria and sooner 

 or later is penetrated exposing the skeletal musculature which becomes 

 markedly hyalinized. Bacteria continue to grow in the accumulation of 

 necrotic debris resulting from the death and subsequent destruction of 

 muscle bundles (Fish 1934). Davis (1946) contradicts Fish (1934) on 

 this point, saying that there is little evidence of undermining of 

 deeper muscles so characteristic of f urunculosis . A possible truth of 

 the matter ma^^ be that the underlying musculature may or may not be 

 destroyed according to the virulence of the organism and susceptibility 

 of the host. 



Recently, Snieszko and associates (1951) have reported that 

 terran^rcin is effective in the treatment of ulcer disease in brook trout. 

 They found that the proportion of surviving trout depended on the rate 

 of mortality at the onset of treatment; if this was not too high, results 

 were good. Aureomycin had no therapeutic value. Sulfonamides have 

 previously been shovm to be unsatisfactory (Tunison and McCay 1937, 

 Wolf 1939 and others). 



CONTROL 



Within recent years ^ with the increase in production of legal- 

 sized trout at a comparatively high cost, the necessity of preventing 

 and controlling fish diseases has assumed major importance. Our 

 knowledge of the methods of prevention and elimination of fish diseases 

 has increased considerably but there is still much to be learned. Some 

 diseases are controlled quite easily, while others, such as furunculosis, 

 are more difficult. The only known method of absolute control of B. 

 salmonicida infection involves complete elimination of all fish from a 

 hatchery, thorough disinfection of the hatchery, the rebuilding of a 

 new stock of disease-free fish, and the maintenance of disease-free 

 conditions throughout all future operations. Unfortunately, this method 

 can only be used at those hatcheries having a controlled water supply, 

 that is, originating in vrells or springs that can be kept free from fish 

 (O'Donnell 1944). 



The measures for the control of furunculosis fall into two groups? 

 (l) the prevention of epidemics, and (2) handling an epidemic which has 

 already started. 



58 



