[181] 



®n tbe Salmon==2)i0ca6e^ 



IN the Proceedings of the Royal Society for the current 

 year, there are recorded some experiments by Professor 

 Huxley, and his observations thereupon, with reference 

 to the parasitic fungus, Saproleg7iia, which has of late wrought so 

 much damage among the Salmon of our rivers ; and as the subject 

 is interesting, both economically and microscopically, we repro- 

 duce them here for the benefit of our readers. 



The body of a recently-killed common House-Fly was gently 

 rubbed a few times upon a patch of the diseased skin of a salmon ; 

 and it was then left for a while in a vessel of water, upon the 

 surface of which it floated, being buoyed up by the air contained 

 abundantly in the tracheae. In the course of about 48 hours, 

 numerous white, cottony filaments made their appearance, set 

 closely together side by side, and radiating from the body of the 

 fly in all directions, so that it presently became inclosed in a thick, 

 white, spheroidal shroud, having a diameter of as much as half-an- 

 inch. These filaments being specifically heavier than water, they 

 gradually overcome the buoyancy of ^the air in the tracheae of the 

 fly, and the whole mass sinks to the bottom of the vessel. The 

 filaments are very short when they first become discernible ; and 

 they usually make their appearance where the integument is 

 softest, as, e.g.^ between the head and thorax, upon the proboscis, 

 and between the rings of the abdomen. In their size, structure, 

 and reproductive arrangements, they are precisely similar to the 

 hyphce of the salmon-fungus ; and the characters of both alike 

 prove that the fungus is a Saprolegnia^ and not an Achlya. It 

 may, moreover, be easily shown that the body of the fly became 

 infected solely by spores which adhered to its surface when rubbed 

 over the diseased skin of the fish. These spores have, in fact, 

 germinated, and their hyphce have penetrated the cuticle of the 

 fly, notwithstanding its comparative density ; and have then 

 ramified inwards, growing at the expense of the nourishment 

 suppHed by the fly's tissues. 



Experiments of this kind, variously repeated with all needful 

 precautions, lead us to the important practical conclusion that the 

 cause of Salmon-disease may exist in all waters in which dead 

 insects, infested with Saprolegnia^ are met with ; — that is to say, 

 probably in all the fresh waters of these Islands, at one time or 

 another; while, on the other hand, Saprolegiiia has never beer; 



