SAPROLEGNIA IN RELATION TO THE SALMON DISEASE. 329 



and be ready to sprinp; into activity as soon as the fish re- 

 turns to fresh water. Cases of the a))pearaiice of the disease 

 in quite fresh-run fish are occasionally reported, which wouhl 

 be readily explicable should this supposition turn out to be 

 well founded. 



Another possibility was suo^jfjested by the same fact. We 

 know that the spores of the Einjmsa, a fun^^us which attacks 

 livino- flies, germinate and bore through the cuticle in much 

 tlie same fashion as the Saprolegnia enters dead flies. But 

 the hypha of the Emjmsa, which has thus entered the fly, 

 immediately breaks up into short joints, which diflfuse their.- 

 selves through the body of the fly and everywhere multiply 

 by division, until they have appropriated all the nutritious 

 matters which are available to them. It was therefore 

 justifiable, on analogical grounds, to suppose that the hyphae 

 of Saprolegnia, which had entered the derma of a saltnou, 

 might break up in a similar way; and that the segments 

 might be conveyed throtigh the lymphatic and blood-vessels 

 into all parts of the body, and either produce blood poisoning 

 by a septic fermentative action, or develop ceutres of 

 obstruction by lodgment in the narrower channels of the 

 vascular system. However, there is no evidence to justify 

 this suspicion. The hyphae in the derma show no signs of 

 division, nor have any toruloid bodies or other structures 

 that can be regarded as derivates of Saprolegnia been 

 observed, either in the blood or in any of the viscera. 



The saltnou disease, in fact, appears to be a purely cuta' 

 neous affectiou ; and the fish seem to die partly from irrita- 

 tion and consequent exhaustion, and partly, perh.ips, from 

 the drain on their resources, caused by the production of so 

 large a mass of vegetable matter at their expense. 



The opportunities for the investigations, the chief results 

 of which have now been detailed, have arisen only during 

 the last three or four months; and a great deal more time 

 and attention must be devoted to the subject before it can be 

 expected that many of the obscurities and difficulties which 

 still hang about it can be cleared up. 



It is needful to discover the conditions under which the 

 fungus exists in those rivers which are infested by the dis- 

 ease when the full-grown salmon have deserted them ; 

 whether it lingers in isolated cases among the parr, trout, or 

 the non-salmonoid fish ; or whether it contents itself with 

 the bodies of dead insects and other dead animal, and per- 

 haps vegetable, substances ; or whether, in the late summer, 

 oosporangia may not be formed and give rise to oospores, 

 which, as De Bary's experiments show, may have a dormant 



