72 I'rauMcUuHii. 



OBSERVATIONS ON THE SALMON DISEASE. 

 By J. Rutherford. 



Bead April 23d, 1880. 



As my communication to this Society last month was oral, I 

 thought it might perhaps be as well to write a paper on the subject, 

 including most of the remai'ks I then made, as well as some little 

 work I have done since. 



1st I will describe the apjiearance of the disease as I have seen 

 it, as clearly and plainly as I possibly can, which I have had 

 confirmed by the examination of a good number of fisL The con- 

 clusions that I have arrived at from those facts and appearances 

 may not be coiTect, as I do not consider my physiological know- 

 ledge sufficient to warrant my assuming that of an authority on 

 the subject. As to the appearance of the diseased fish when seen 

 in the water I need say little, as it must be so well known to the 

 most of you. When they are first seen to be afiected they have 

 one or two small spots generally near or on one of the fins, often 

 the dorsal or tail fins. Those spots gradually extend, until in a 

 number of cases the fish is nearly covered. In the course of time, 

 when the disease begins to aflect the constitution of the fish, they 

 begin to look languid, and gradually draw into the smooth and 

 shallow water at the sides of the river — I believe from a feeling 

 of weakness to resist the current of the stream. The white spots 

 when seen in the river look like mould, such as is generally seen 

 growing on decaying animal or vegetable matter. I have seen it 

 when it looked to be about an inch or so in length. When the 

 fish is taken out of the water that mouldiness assumes a sort of 

 matted, slimy appearance, and can easily be scraped from the 

 scales with a sharp knife or razor, and in most cases leaves no 

 trace by which the eye covUd detect that it had ever been there. 

 A little of the mouldy-looking substance placed under the micro- 

 scope reveals at once the fact that it is a fungus — viz., Saprolegnia 

 ferax, the filaments of which take all sorts of forms. The most 

 of other plants can be at once known by the form which they 

 almost universally take, but not so with S, ferax. This fungus 

 takes all imaginable forms for its filaments. I have made (partly 



