SAPROLEGNIA IN RELATION TO THE SALMON DISEASE. 323 



2-ith of jMarch from a culture on bladdtr, which was again 

 derived from a fly infected directly from a North Esk salmon 

 on the 14th of March. 



It may be safely concluded, therefore, that the salmon 

 fun<Tus is not a parasite peculiar to that fish, but that it is a 

 form of the Saprolegnia ferax, which, so far as our observa- 

 tions go — and it must be remembered that these extend over 

 only the quarter of the year between Christmas and the 

 snring equinox — remains devoid of oosporangia so long as it 

 infests the fish, and tends to persist in this condition for a 

 long time, even when it is cultivated on those matters upon 

 which the Saprolegnia more usually subsists. Future ob- 

 servation must determine whether oosporangia are developed 

 on the Saprolegnia, while still growing on salmon, later in 

 the year. The evidence of the fact at present extant is ex- 

 tremely unsatisfactory ; and it is a remarkable circumstance 

 that the figures which have been published show no trace of 

 antheridial filaments. 



That living fish may be attacked and destroyed by epi- 

 demic diseases, of which a Saprolegnia is either the cause or 

 the constant accompaniment, has been known for a very long 

 time. 



Forty years ago the eminent German botanist, linger,^ 

 described a disease which broke out among some carp in a 

 pond in the Botanic Gardens at Gratz, and was obviously 

 caused by a fungus, at that time known as Achlyaprolifera, 

 but which the description and figures given by Unger clearly 

 prove to belong to the genus which is now distinguished as 

 Saprolegnia, and, indeed, to be very similar to, if not identical 

 with, S.feraz. More or less distinctly circumscribed pale 

 spots appeared upon the skin of the back and of the fins. 

 The fish became sluggish and sought the surface of the 

 water. A velvety investment, formed of very delicate, 

 colourless, close-set threads, showed itself on the spots 

 affected, which rapidly became confluent, and extended from 

 mouth to anus, and even on to the gills. The scales of the 

 affected parts became detached, red, and swollen, and some- 

 times ulceration occurred. The animals could no longer 

 move without appearing to suffer great pain ; they remained 

 at the surface of the water, lying either on their backs or 

 on their sides, and death took place in eight-and-forty hours. 

 Unger found that the disease could be transferred to perch 

 by inoculation. 



Again, there seems no reason to doubt that the fungus 



^ " Sur I'Acblya prolifera," * Annales des Sciences Naturelles, Botanique,' 

 serie iii, 1S44. 



