The Fungus of Salmon Disease. 73 



ravages may be found easier ; and this is not unnatural to 

 believe, as the disease in all rivers seems to appear suddenly, 

 and to cause the death of a varying number of fish, after which 

 it will die out, and then for months not a case of disease is 

 heard of. Now, the spores of the disease, as before explained, 

 must remain in the river during the time that the disease is 

 not prevalent, and the pertinent question is then forced on us, 

 " Why are the fish not liable to the disease all the year round ?" 

 The partial explanation of this, I venture to think, is that the 

 temperature of the water is one cause, together with coincident 

 conditions that are of almost equal weight. In giving this 

 as my opinion, let it be understood that my experience re- 

 fers to a river where the outbreak of the disease is very different 

 from the epidemics in England or elsewhere that I have read 

 descriptions of, as it occurs in summer instead of winter, and 

 attacks clean run fish instead of spawning salmon or kelts ; 

 though the important point of a few fish dying in winter also 

 in the same river ought not to be forgotten. 



That our salmon disease fungus will develop far more rapidly 

 in summer than in winter is, I think, beyond doubt. Labora- 

 tory cultivation of the fungus never fails to show this clearly ; 

 but if a proof be necessary, let a piece of diseased skin be taken 

 off a salmon from a river where the water is under 50 Fahr. ; 

 put it in a glass vessel with clean water, and transfer it to a 

 warm room, where the temperature is about 6o° or 65 Fahr. 

 Under these conditions I have seen the stimulus of heat cause 

 a second growth under the first, and the line of development in 

 such growth clearly defined to the naked eye. It has been said 

 that temperature seems to exercise no influence, as the disease 

 can go on causing destruction during the coldest weather ; 

 and this, when referring to winter attacks, is quite correct, as 

 far as it goes, in proving that the fungus can develop even in 

 the cold quickly enough to kill fish ; but in these cases the 

 many other coincident conditions on the side of the fish must 

 be extremely unfavourable, and would only suggest that with 

 warmer water, and other conditions remaining the same, the 



