14 



One of these fish escaped. " The other died on the i6th 

 of March, its body being nearly covered with a luxuriant 

 growth of Saprolegnia ferax" Two other fish similarly 

 infected died, the one in ten days and the other in fourteen 

 days. This, so far as I know, is the first direct evidence 

 that the Saprolegnia of the salmon disease is capable of 

 being transmitted from dead insects to living fish of 

 other kinds. 



Combining these observations with those made on the 

 epidemic among carp by Unger in 1844, and with those of 

 Stirling on the fish in the Ightham ponds, I begin to doubt 

 whether any other fungus than Saprolegnia attacks fishes. 

 A distinction is often drawn between the " aquarium fungus " 

 and Saprolegnia. But within a few days of the opening of 

 this Exhibition, the trout and char in the freshwater 

 tanks were largely attacked by " aquarium fungus," and I 

 took the opportunity of subjecting fresh specimens to care- 

 ful examination. I found it to be all Saprolegnia ferax, 

 and I could cultivate it on flies just as well as the salmon 

 Saprolegnia. As yet, I have met with no satisfactory 

 evidence that the integument of fishes is attacked by any- 

 thing but Saprolegnia. 



The Saprolegnia is essentially a freshwater organism, 

 which dies as soon as an infected fish reaches salt water. 

 As, however, it is only the exposed part of the fungus 

 which comes into contact with the sea water, it was possible 

 that the hyphae, which are embedded in the true skin, 

 might retain their vitality during the sea life of the fish, 

 and make their appearance at the surface on its return to 

 fresh water. And, when I made my first report on the 

 disease, I thought it possible that the key to the mystery ot 

 the appearance of the disease in fish just returned from the 

 sea might lie here. 



