at 219 Co does not appear to be due to lessened activity of the organism 

 itself = The Purunculosis Committee (1933) feels that it is doubtful 

 whether the greater incidence of infection at about 15° Co under conditions 

 of e3q)eriment can be exactly related to the optimum temperature for 

 grcwth of Bo salmonicidao They add that an important factor is the time 

 an infecoed fish takes to die of the diseasSn which m turn is dependent 

 on the height of the temperature c Thus, a fish cfying rapidly probably 

 contaminates its surroundings to a lesser degree than one in which the 

 illness is prolonged. The optimum temperature for spread of the disease 

 may be dependent therefore not on one factor but a combination of 

 influences acting togethero At very low temperatures^ it is probable 

 that the direct effect of temperature on the bacteria is a factor which 

 lessens the chance of iri^ectiono 



Water pollution 



In Great Britain the majority of epizootics have taken place 

 where pollution is either infinitesimal or nonexistent (Ftu^unculosis 

 Committee 1930)o In the Tweed f Scotland), a heavily infected river in 

 certain parts„ the incidence of the disease was so slight that only by 

 chance has it been identified. Only in the Lledr (England), an infected 

 tributary of the Conway., and in some of the sou them trout streams in 

 which the disease has occurred., was pollution stated to be of any 

 importance o In Great Britain, funanculosis has not been found to be 

 restricted to any particular type of river but has occurred in chalk and 

 peat water, in mountain streams almost free from pollution and in 

 heavily polluted rivers (Blake and Clark 1931 )» Home (19^8) found no 

 distinct relation be".^een high bacterial content of water and the 

 presence of the disease., and an his viability studies could not recover 

 the organism from sewage after 48 hours o 



Plehn (1924.)v or- the other han.d. found not only that Bo 

 salmonicida surv'-lved longer in polluted than in pure water„ but also 

 that the danger of infection increased according to the quantity of 

 pollution by organic matter o According to her effluents from breweries 

 distilleries and dairies are mcst harmful and in them the disease takes 

 its worst form.. In support of Plehn 's (192/i.) view., Duff (194-0) showed 

 that Bo salmonicida sur-vived 15 days in undiluted fresh sewage and at 

 least 30 days in diluted autoclaved sewage. 



It becomes evident at once that not only is the information 

 regarding the relation of the prevalence of furunculosis to pollution 

 contradictory but that the problem is also a complex one.. It appears 

 that the crux of the matter resides in the nature of the pollution. 

 Sewage high in organic content might well favor the survival of B. 

 salmoni clda partly in itself and partly by enhancing growt-h of other 

 flora^ bacterial and ot.he.rwise , already present in fresh water^ thus 

 favoring the development of a severe epizootic. On the other hand., 

 noxious inorganic matter (such as found in trade wastes) might well cut 



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