SAPROLEGNIA FERAX, SALMON DISEASE. 149 



same position for weeks together, and yet saprolegnia 

 has never made its appearance in the Galway river. 

 On making inquiries I ascertained that a disease 

 somewhat similar in appearance, as described to me, 

 broke out on one or two occasions during summer, 

 when the water was very low, but no fish died from it, 

 and it soon disappeared. 



One significant fact in connection with saprolegnia 

 seems to have escaped general attention. There 

 is neither report nor record of the occurrence of this 

 disease in Ireland. The cause of this exemption 

 should prove an interesting problem for scientists. 

 Independently of this, however, there is what appears 

 to me to be an unanswerable argument against the 

 theory that saprolegnia is originally due to over- 

 crowding, viz. that it sometimes breaks out in rivers 

 in which salmon are scarce, and in which it is hardly 

 possible under any circumstances that the pools could 

 be overcrowded with salmon. 



Pollutions of all kinds are more or less injurious 

 to fish ; some contain the most deadly poison, and 



