
THE, SALMON DISEASE. T55 

be a Saprolegnia and not an Achlya. Moreover, Prof. Huxley 
states that it was easy to obtain evidence that the body of the fly 
was infected by the spores swept off by its surface when it was 
rubbed over the diseased salmon skin. 
Saprolegnia has never been observed on decaying bodies in salt 
water, and there is every reason to believe that as the saprophyte 
it is confined to fresh water. Prof. Huxley says that, so far as he 
is aware, there is only one case on record of the appearance of 
fungus on fish in salt water, and in this case it was not certain that 
the fungus was Saprolegnia. 
Thus it becomes evident, or at least highly probable, that the 
origin of the disease lies in spores of Saprolegnia which emanate 
from dead organic bodies in our fresh waters. 
Having infected dead flies with salmon Saprolegnia once from 
Conway and once from Tweed fish, Prof. Huxley fancied it would 
be easy to determine the exact species with which he was dealing, 
but the experiments were not thoroughly satisfactory, and although 
from the result of them he has very little doubt that the Sapro- 
Zegnia of the salmon is one of the forms of the S. fevax group of 
Pringsheim and De Bary, he has at present no proof of the fact. 
A curious and unexpected peculiarity of the salmon Saproleguia, 
both on the fish and when transferred to flies, is that locomotive 
ciliated zoospores do not appear, but whether the season of the 
year or the conditons under which the saprolegnised flies were 
placed had anything to do with their non-appearance he cannot 
say. Whether the zoospores are actively locomotive or not, they 
are quite free when they emerge from the zoosporangium, and, 
from their extreme minuteness, must be readily disseminated 
through the surrounding water. Hence a salmon entering a stream 
inhabited by the saprophyte will be exposed to the chance of 
coming in contact with saprolegnia spores. At a vety moderate 
estimate, a single fly may bear 1000 fruiting hyphz, and if each 
sporangium contain 20 zoospores, and run through the whole 
course of its development in twelve hours, the result would be the 
production of 40,000 zoospores in the day. It appears that 2,000 
diseased salmon have been taken out of a single comparatively in- 
significant river in the course of the season. 
There are many practical difficulties in the way of directly ob- 
serving the manner in which the zoospores effect their entrance 
into the skin of the fish and the structure of the healthy integu- 
ment is dealt with in Prof. Huxley’s paper. It appears that sections 
of young patches of diseased skin shew that the hyphe of the 
fungus not only traverse the epidermis but also bore through the 
superficial layers of the derma, in some cases as much as 7’p of an 
inch. In the derma the root hyphz branch out, pierce the bundles 
of connective tissue, and, usually, end in curiously distorted ex- 

