The Fungus of Salmon Disease. 69 



was necessary to work in a different way and with far greater 

 precaution. 



The conditions of laboratory cultivation, when carried on in 

 the manner I have described, offer, when compared with the 

 disease as it occurs in a river, one obvious difference. I refer 

 to the important circumstance of river water always being in 

 motion, fresh and well aerated ; while in artificial culture the 

 unfavourable conditions of stagnation are always more or less 

 present. This difference is, of course, all in favour of the river 

 as a situation for the fungus to develop in more favourably, and 

 by reason of other competing organisms, which are generally 

 free in the liquid, being carried away by the currents, while the 

 fungus, attached to the fish by its roots, remains in undisputed 

 possession. 



For this reason, it is evident that the salmon disease ought 

 to be studied on the fish themselves as well as by laboratory 

 cultivation. The observer ought to have, besides the fullest 

 local information, every opportunity of examining and studying 

 the varying conditions that surround the fish at the time of 

 their immunity from the disease, as well as during epidemics. 

 By such experience he would probably be able to collect evi- 

 dence having direct bearing on the disease, instead of puzzling 

 and contradictory reports, which are all that we at present 

 possess. 



The fungus of salmon disease is the same all over the king- 

 dom. Most observers agree that in every river the type is 

 identical. My own observation on this point is not confined 

 to the disease as it occurs in Ireland. I have had the Scotch 

 and English fungus under observation for long periods, and 

 cannot observe any morphological or other difference at any 

 stage of development. The variety is probably Saprolegnia 

 torulosa. Each kind of the fungus, whether Irish or English, 

 will occasionally assume differently-shaped sporanges under 

 varied conditions of culture. 



It is within the bounds of possibility that the salmon disease 

 fungus could be made, by a series of adapting cultivations 



