BULLETIN OF THE UNITED STATES FISH COMMISSION. 437 



the course of all his iuvcstigatioiis ; and not a single specimen has pre- 

 sented itself in the considerable number of diseased salmon from the 

 Conway, the Tweed, and the Xorth Esk, which have come under our 

 observation during the last four months. 



When our inquiries commenced, there was, strictly speaking, no proof 

 that the salmon Saprolegnla could live on anything but a salmon. It 

 was, therefore, quite possible that, since there are many species of 

 Saprolegnia,, that of the salmon might be peculiar to it, just as, in the 

 analogous case of the potato disease, Peronospora infestans is different 

 from all the species of Fero)iosp)ora, which abound upon European wild 

 plants, and will not live on them any more than these other species will 

 live on the potato. 



However this may be, it is easily proved that the Saprolegnia is not 

 dependent on living salmon. In fact, if a patch of diseased skin is cut 

 off" and placed in a vessel of water it will be found in twenty-four hours 

 to be covered with a new growth of young hypha?, close set, and of nearly 

 equal lengths, so that the surface resembles a miniature cornheld. A 

 I)iece of the diseased membranous valve of the mouth of a salmon was 

 placed in water on the 4th of March, 1882 ; on the Gth it was covered 

 with young hyphse one-fifth of an inch long ; and on the 7th these had 

 elongated and developed multitudes of zoosporangia. 



Moreover, there is not the least difificulty m proving that the salmon 

 Saprolcf/nia is not dependent upon salmon at all, but that it is ca])able 

 of living on dead insects and pieces of wet bladder. If a recently killed 

 fly is gently rubbed two or three times either over a fresh patch of dis- 

 eased salmon skin, or over one which has developed the fresh growth 

 just mentioned, and then placed in a vessel of water by itself, it will be 

 found in the course of eight-and-forty hours to be more or less exten- 

 sively beset with short delicate cottony-looking filaments, which rapidly 

 increase in length and in number until, at last, the fly's body is inclosed 

 within a spheroidal coat half an inch in diameter. These filaments are 

 hyphse having exactly the same size, form, and structure as those of the 

 salmon Saprolegnia ; their ends give rise to zoosporangia of the same 

 character ; and these produce zoospores of the same size, which germi- 

 nate in the same way. 



Between December, 1881, and April of the present year, repeated 

 experiments of this kind have been made with diseased salmon from the 

 Conway, the Tweed, and the Korth Esk, upon dead flies, and small 

 pieces of wet bladder, always with the same result. There appears, 

 therefore, to be no doubt that the ISaprolegnia of the salmon, like other 



Mr. W. G. Smitli, in a paper on the salmon disease in the " Gardener's Clironicle," 

 May 4, 187d, not only affirms that " the resting spores are common enough," but figures 

 them. However, Mr. Smith's figures of the zoosporangia are so unlike anything 

 ordinarily observed in the salmon Saprolegnia, and his statement that "the fungus has 

 invariably vanished with the death of the fish." is so strangely contrary to common 

 experience, that it is difficult to know how much weight ought to be attached to his 

 observations. 



