388 On the Epidemic known as the " Salmon Disease." [Mar. 2, 



gradually takes place, small vessels give way and bleed, and the 

 burrowing sore, which, is characteristic of the advanced stages of the 

 disease, is produced. 



The skin of the head may thus be eaten away down to the bone 

 and gristle of the skull, but I have not observed the fungus to 

 enter these. On the scaly part of the skin, the fungus burrows in the 

 superficial and in the deep layer of the pouches of the scales, but I 

 have not observed the scales themselves to be perforated. 



When I found that the fungus penetrated the true skin, and thus 

 gained access to the lymphatic spaces and blood-vessels, it became a 

 matter of great interest to ascertain whether the hyphae might not 

 break up into toruloid segments (as in the case of the Emjpusa muscce) , 

 and thus give rise to general septic poisoning, or fungoid metastasis. 

 However, I have never been able to find any indication of the occur- 

 rence of such a process. 



But a very important practical question arises out of the discovery 

 that the fungus penetrates into the derma. There is much reason to 

 believe, that if a diseased salmon returns to salt water, all the fungus 

 which is reached by the saline fluid is killed, and the destroyed 

 epidermis is repaired. But the sea water has no access to the hypha3 

 which have burrowed into the true skin ; and hence it must be 

 admitted to be possible, that, in a salmon which has become to all 

 appearance healed in the sea, and which looks perfectly healthy when 

 it ascends a river, the remains of the fungus in the derma may break 

 out from within, and the fish become diseased without any fresh 

 infection. It has not infrequently been observed, that salmon in their 

 upward course became diseased at a surprisingly short distance from 

 the sea, and it is possible that the explanation of the fact is to be 

 sought in the revival of dormant Sajprohgnia, rather than in new 

 infection. It is to be hoped, that experiments, now being carried on at 

 Berwick, will throw some light on this point, as well as upon the 

 asserted efficacy of sea water in destroying the fungus which it 

 reaches. 



These are the chief results of this season's observations on the 

 salmon disease. Incomplete as they are, they appear to me to justify 

 the following conclusions : — 



1. That the Saprolegnia attacks the healthy living salmon exactly 

 in the same way as it attacks the dead insect, and that it is the sole 

 cause of the disease, whatever circumstances may, in a secondary 

 manner, assist its operations. 



2. That death may result without any other organ than the skin being 

 attacked, and that, under these circumstances, it is the consequence 

 partly of the exhaustion of nervous energy by the incessant irritation 

 of the felted mycelium with its charge of fine sand, and partly of the 

 drain of nutriment directly and indirectly caused by the fungus. 



