348 JOURNAL OF SCIENCE. 
disease from the epidermis and restores the fish to apparent 
health, yet on its re-ascent of the river the disease, if it has pre- 
viously penetrated the true skin, reappears on the fish, with or 
without the accessory of fresh infection. Sir James Gibson 
Maitland also, in his essay sent to the Norwich Fishery Exhibi- 
tion, 1881, has contributed some very useful information. He 
says :—“ Saprolegnia ferax is one . those fungi which propagate 
either by seed or cells. The cell is in diameter many times larger 
than the seed, and is probably always present at all times in all 
waters ; but there is this difference between the two modes of 
propagation—the cell is much more particular as to the soil on 
which it can root than the infinitesimal seed. Wherever there is 
dead fish matter in water the fungus is sure to grow, but unless 
some scrape or sore form a suitable nidus, I very much doubt 
if it would grow from the cell on the back of a living fish. It is 
probable zoospores are fertilised by the actual penetration of the 
male spore, and in this fertilisation the secret of the epidemic 
probably lies. I mean I consider the zoospore the cause of 
epidemic, the resting-spore the cause of after-growth in the 
sporadic form of the disease, and the probable source of the cen- 
tres of infection from which the epidemic spreads.” But the 
most important and suggestive observations are those of Mr. 
Livingstone Stone, given in his “ Domesticated Trout, 1877.” 
In Appendix I. Mr. Stone says :—“It has hitherto been sup- 
posed, I believe, that the fungus eats into the tissues of the fish 
and destroys it. The microscope revealed, however, that it was 
not the fungus that penetrated into the fish, but a multitude of 
microscopic worms of the shape and appearance given on page 
278. The worms are never found in the upper part of the fun- 
cus, but just below the roots, or where the fungus joins on to the 
surface of the skin. They are about 1-8o0th of an inch in length, 
and 1-200th of an inch in diameter, and are provided with a mouth 
at one extremity, and at the other with about twenty claw-like 
appendages for fastening on to the fish on which they feed. They 
are continually eating into the tissues of the fish, and the twenty 
tentacles enable them to fasten on so tightly that the fish cannot 
shake them off. These parasites appear to live on the flesh of 
the fish, and the fungus to live on the digested matter into which 
they transform it.” 
There appear to be two or more different species of fungi 
which attack the Salmonidz ; but the particular form described 
by Mr. Stone has not as yet been identified on any diseased sal- 
mon examined in England. Probably it is not the same; but, 
be that as it may, it is sufficient for my present purpose that the 
salmon disease is due to a fungus, which microscopists call Sapro- 
legnia ferax, and that it is epizoic—that is, fastens on to the skin 
of the fish, and from the outside strikes its roots into the tissues. 
2. A summary of the occurrence of the Salinon disease, and of the 
conditions of different waters—The evidence taken by the Com- 
missioners disclosed the fact that the disease has been known to 
