FUNGUS DISEASE AFFECTING SALMON. 529 



ramify in the mucous and epidermic layers of the fish ; they do not pen- 

 etrate the corium where there are no scales. In other situations they 

 never reach a greater depth than the outer surface of the scales ; they 

 are tubular. The whole plant, being without sejita, forms a single in- 

 dividual of apparently indefinite extent. The spores are variously 

 shaped at different stages, ovate and kidney being the commonest forms. 

 They are very minute, and require a power of 450' diameters to observe 

 them well. The cilia are two in number, a longer and a shorter one, and 

 are situated at the long axis of the spore. They are difficult to observe, 

 and always disappear in permanently-mounted preparations, although 

 the spores themselves remain unaltered in all other respects. When the 

 fungus is stained with logwood or i)icric acid, excellent i)ermanent pre- 

 parations can be got. It has been stated that the fungus dies with the 

 fish. I have not found this to be the case ; on the contrary, all my obser- 

 vations have been made from dead fish. Some of the specimens sent me 

 from Carlisle by Mr. Dunne were missent to Aberdeen, and returned to 

 me on the seventh day after the death of the fish, and yet I have scores 

 of permanent preparations from these specimens which show distinctly 

 the characteristic form of Saprolegnia ferax. 



I have also found the fungus perfectly identical in all the specimens I 

 have examined, which consist of salmon, sea-trout, and river- trout from 

 the Eden, and salmon and grayling from the Mth. 



It has also been said that a salt solution destroys the fungus, " which 

 melts in the solution like sugar in water P On the contrary, salt and water 

 is an excellent preservative of Saprolegnia; masses of it before me as I 

 write have been in a salt solution for two months, and it remains unal- 

 tered. Further, the salmon captured in the Mth, which is believed to 

 have gone to the sea in order to get rid of the fungus, had the fungus 

 growing vigorouslj^ on several parts of its body. The fungus must either 

 have instantly attacked the fish on its return to the river, or not have 

 been destroyed during its stay in the salt water. 



Regarding the cause of the disease, I can offer no opinion further than 

 that some functional condition of the fish seems necessary for the prop- 

 agation of the fungus. The germs of Saprolegnia ferax must exist at aU 

 times and in many i^laces ; and, if so, there must be a reason why fish 

 are not constantly affected with the fungus and in every river. I am 

 persuaded that the condition of the fish is in some way either suitable or 

 unsuitable for the propagation and growth of the fungus. Whether this 

 arises from too high or too low condition, I am quite unable to say ; but 

 I may remark that while some of the fish examined were in the kelt 

 stage, others were in a condition perfectly fit for food. 

 34 F 



