I he Fungus of Salmon Disease. 79 



free from the epidemic, and that among these rivers are some 

 which are so contaminated for long distances from the sea as to 

 cause wonder when we think that salmon can live to ascend in 

 them — instance the Liffey. 



If pollution exercised a directly favourable influence on our 

 fungus, the ordinary outbreaks of the disease ought to occur 

 during the summer, when such impurity is concentrated ; but, 

 instead, we find that the virulent outbreaks of the disease 

 occur during the winter, when by the prevalence of floods the 

 pollution must be reduced to its maximum dilution, with water 

 often running banks high all the time. 



I am convinced that any injury resulting from pollution must 

 be expended on the fish themselves, and only think it possible 

 that conditions perhaps favouring the fungus may be thus in- 

 directly brought about. Impure water cannot be favourable to 

 the fungus any more than to the salmon ; but when it only 

 exists near the mouths of rivers, and the fish have ample oppor- 

 tunity of ascending to good water for their spawning opera- 

 tions, there is probably not much injury done. If so, it is the 

 more to be regretted, as nearly all our salmon rivers are more 

 or less polluted near their outlets to the sea, and some of them 

 to a horrible extent. Overcrowding of fish in holes could not 

 well cause the disease, although this is frequently believed. 

 Such a theory only finds support when absolute contact of the 

 fish one with another is considered necessary, and this is not 

 the case unless with perfect fish, having their epidermis unin- 

 jured, and when a diseased fish might infect or inoculate a 

 perfect one with a blow, or rubbing movements, which would 

 plant the spores in its skin. Such an influence as acidity or 

 alkalinity can certainly have bearing on organic life, but rigid 

 research with our fungus does not inform us in any definite 

 way whether the influence would be favourable or not. The 

 probability is that both fish and fungus might die under it, 

 the fungus first, and both be consumed by a race of bacteria 

 better suited to the circumstances. The salmon disease fungus 

 is (if it may be so called) a decidedly clean feeder, and decaying 

 organic matter or sewage pollution would certainly be unfavour- 



