154 THE HABITS OF THE SALMON. 



" Fungi are also extremely sensitive to slight 

 differences in the acidity or aljs;alinity of water, so 

 that even apparently insignificant changes in this 

 respect may come into play as secondary conditions 

 of salmon disease. 



" Hence, although there is not the slightest ground 

 for regarding ' pollutions,' whether they arise from 

 agricultural or manufacturing industries, as primary 

 causes of salmon disease, they may have a most 

 important secondary influence ; they may, in fact, 

 determine whether in any river the disease shall be 

 sporadic or epidemic." 



Taking, therefore, the foregoing statement into 

 consideration, I think it may safely be assumed that 

 pollution of some kind, the nature of w^hich has yet 

 to be discovered, is indirectly, if not directly, the 

 cause of the disease called Saprolegnia ferax. 



Attempts have been made to stamp out salmon 

 disease, by removing from the rivers all diseased 

 fish that can be laid hands on, and burying them or 

 otherwise destroying them. When disease breaks 



