109 



" keep nature's numerous family in a prosperous and healthy condition."* 

 We might inquire which has destroyed the largest per-centage of fish, the otter 

 or the disease ? Which left the survivors in the best condition to fight the 

 battle of life in the succeeding seasons? Probably few would hesitate to 

 welcome back the otters if they could be assured that thereby the disease could 

 be controlled. Yet we may rest assured that it is hopeless thinking of killing off 

 the fungus. We have not killed the potato disease, and no prospect of doing 

 so. If success is to be at all achieved it must be by restoring to the salmon 

 such a constitution as will enable it to defy the attacks of its parasites. 



Remedies. — I have already said enough to obviate any suspicion that I 

 intend to propose any universal panacea. Suggestions affecting what I have 

 termed " secondaiy causes " are all that I would offer, and these would suggest 

 themselves to practical men more readily than words of mine, if they will 

 accept the definition of secondaiy causes as sufficient. If the annual recur- 

 rence of the disease is destroying the constitution of the salmon, it must as a 

 consequence follow that the disease will increase rather than diminish, unless 

 some means of invigorating the salmon can be found. If the parents are 

 becoming debilitated, how can a healthy offspring, or a robust future genera- 

 tion be anticipated from the same stock. If obstructions in the rivers become 

 still more formidable when they have to be encountered by a weakened race, it 

 will soon become a question of " salmon or no salmon." If badly diseased, or 

 dead fish, are permitted to remain in company with the living, it only increases 

 enormously the risks of the healthy fish. The destruction of all the diseased 

 fish in any river would not by any means imply the destruction of the disease, 

 especially so long as the secondary causes remain unchanged. Low waters are 

 not to be improved by Act of Parliament, but with low waters follow longer 

 leaps to overcome increased distances at the weirs, and ordinary obstructions 

 attain extraordinary dimensions. These are questions which are scarcely within 

 my province, and as the task to which I applied myself has been accomplished, 

 however imperfectly, I may leave what I have written to a careful and candid 

 consideration, in the hope that it may prove of some service in an excellent 



cause. 



M. C. Cooke, M.A., LL.D., A.L.S. 



146, Junction Road, N. 

 June 1, 1880. 



DR. M. C. 

 COOKE. 



II.— Letter from C. L. Jackson, Esq., Consulting Naturalist to The 



southport aouarium. 



Gentlemen, 



I have watched with great interest the progress of the investigations 

 into the nature, probable cause, and question of cure of the salmon disease or 

 fungus. I have not hitherto joined in the discussion or advanced any theory, 

 as I have thought all along that microscopic examinations alone_ and post 

 mortems on dead fish would not throw a very clear light on the subject, and I 

 did not see how the disease itself in its rise, progress, and symptoms could well 

 be watched ; chance has, however, enabled me to do this to some extent. I 

 regret extremely, that owing to your having to present your report, I must send 

 you my observations now, for there are still several points which only some 

 weeks watching and experiments can clear up. Ultimately I hope to let you 

 have all the information I have been able to get. 



A very serious outbreak of Saprolegnia ferax among our fresh-water fish at 

 Southport Aquarium has afforded me the opportunity of observing the disease 

 in all its stages, and in its different phases. 



One question in connexion -with it is whether it is a new disease or 

 merely the old aquarium fungus. I have no hesitation in saying it is a fresh 

 disease, or, if it has been known before, it is not our old friend. I am well 

 acquainted with the old pest. In the earlier days of our aquarium we were 



MR. C. L. 

 JACKSON. 



* Land and Water, May 8, 1880, p. 401. 



