194 ON THE SAPROLEGNIEiE. 



the Saprokgnia, and not the cause. A third view is that taken by 

 Erasmus Wilson, who considers that the fungus is a morbid growth 

 of the mucous produced by the skin of a diseased animal, and not 

 a vegetable parasite, and that it closely resembles ringworm in the 

 human subject, in which also there is a fungiform growth. 



Cooke, in commenting upon this view, says : — " I should be 

 most willing to believe with those who assert that the salmon- 

 disease is a contagious disease, which spreads from fish to fish, 

 producing blotches or eruptions, upon which a parasite afterwards 

 estabhshes itself. It is certainly not an impossible cause, and none 

 of the evidence really contradicts it, but I fear that is all which 

 can be said in its favour. A single fish, with the skin and flesh 

 diseased in the identical manner as in the ordinary disease, but 

 from which the fungus was wholly absent, would suffice to prove 

 that the fungus is not the cause of the disease. In the absence of 

 this single evidence, I am afraid I must confess that, as far as we 

 at present know, the fungus appears to be the active agent in the 

 salmon-disease." 



Huxley says : — " Close up to the free ends of the mycelium 

 the epidermis is perfectly healthy, and this fact suffices to prove 

 that the growth of the fungus is the cause of the morbid affection 

 of the epidermis, and not its consequence. If it were otherwise, 

 the structural alteration of the skin should precede the fungus, and 

 not follow it, as it actually does. 



It was at one time thought that the Salmon Saprolegnia could 

 not live on anything but a salmon ; but Huxley has demonstrated 

 that dead flies, and pieces of bladder, can be infected with the 

 spores of the Salmon Sapi'olegnia^ and will produce, in a short 

 time, a fungus growth indistinguishable from the original plant, 

 and he was able, by constantly infecting fresh material, to keep up 

 a supply of the fungus from the end of December to the first 

 week in April. From this study of its life-history, he was able to 

 form the conclusion that the Saprolegnia of the salmon, like other 

 Saproiegniece, is capable of living and flourishing on a variety of 

 dead animal matters. De Bary, in his last researches, also 

 infected meal-worms with the fungus. It seems probable that 

 Saprolegnia is killed by salt water, so that the injured epidermis 

 may heal when a diseased fish enters the sea. But as the myce- 



