II 



site, is it identical with the Saprolegnia already well known 

 as a saprophyte ? 



It was for this purpose that I went to Bettws-y-Coed, in 

 the winter of 1881, in order to study, on the fresh fish, the 

 nature of the epidemic of salmon disease which had broken 

 out in the Conway ; and I soon obtained the evidence I 

 sought, for by examining the margins of moderate-sized 

 fresh patches on the heads of salmon, it was not difficult to 

 demonstrate that the patch of fungus constantly extends 

 at the periphery by sending out fresh hyphse into the 

 healthy epidermis, which it breaks up and destroys ; at the 

 same time, it drives into the subjacent vascular true skin 

 hyphse which play the part of rootlets ; these, ramifying in 

 the superficial layer of the true skin, give rise to sloughing. 

 If a single strawberry-plant is set in the middle of a bed, 

 it will send out runners in all directions, and these will 

 strike root into the soil wherever they go until the whole 

 bed is covered. The Saprolegnia patch grows in a some- 

 what analogous fashion, but its " runners " and " roots " 

 destroy the living tissues in which they are lodged. 



These observations left no doubt in my mind that the 

 Saprolegnia is the cause and not a mere accompaniment 

 of the salmon disease that the latter is in fact what 

 pathologists term a mycosis. And with respect to the other 

 point, namely, the identity of the parasitic with the sapro- 

 phytic Saprolegnia, I found it easy enough to obtain 

 equally conclusive evidence. 



If the salmon Saprolegnia was the same as that which 

 commonly grows on dead insects, it is obvious that one ought 

 to be able to sow dead insects with it and raise a crop of 

 the fungus on them ; and in fact nothing is easier than to 

 do this. Fill a clean tumbler three parts full of clean 

 spring water, and provide it with a loose paper cover ; then 



