i8 



in its saprophytic form in most fresh waters, and that it 

 attacks the fish of most rivers occasionally. In other 

 words, the mycosis of freshwater fishes is a widespread 

 sporadic disease. 



7. That which it is now desirable to ascertain, is the 

 nature of the influences under which the sporadic disease 

 suddenly assumes an epidemic character. 



On this point we have very little light at present, for 

 although there is some reason for thinking that deficient 

 oxygenation, whether produced by overcrowding or other- 

 wise, may favour the development of the disease, and 

 though it is possible that some kinds of pollutions may 

 favour it, yet the disease sometimes becomes epidemic 

 under conditions in which these two predisposing causes 

 are excluded; and it does not always appear when they 

 are present. 



8. Epidemics subside spontaneously, though the fish 

 remain in fresh water. 



9. The productiveness of a salmon river is not neces- 

 sarily interfered with by even a violent epidemic. 



The last three propositions indicate the moral of my 

 paper which is to make sure that you know what you are 

 about before meddling with the salmon disease. Until the 

 causes which convert the sporadic into, the epidemic disease 

 are known, all interference is mere groping in the dark ; and 

 when they are known, it will be a great question whether 

 the preventive measures adopted are worth their cost. 



Fishery doctors at the present day remind me of human 

 doctors in my youth they were always for doing something. 

 I remember one of my teachers laid down the notable 

 maxim, "when you are in doubt, play a trump," and I 

 should think that those of us who have followed his advice, 

 in the last forty years, must have largely added to the 



