SAPROLEGNIA FERAX, SALMON DISEASE. 153 



on fresh-water fishes, and the two forms are alto- 

 gether so similar, that conditions analogous to these 

 which stimulate the growth of the one may be 

 assumed to favour that of the other. 



" Brefeld has pointed out that there is no better 

 medium for the culture of fungi of all sorts, than an 

 infusion of dung. 



" Land under high cultivation undoubtedly supplies 

 the waters in its neighbourhood with something that 

 nearly answers to an infusion of dung ; and this 

 must be taken into account in discussing the possible 

 factors of salmon disease. 



" Again, it is known, with respect to many of the 

 common moulds such as Pencillium and Mucor which 

 are habitually saprophytes (that is to say live on 

 decaying organic matter as saprolegnia does), that 

 they flourish in certain artificial solutions containing 

 salts of ammonia. 



" It is quite possible, though whether the fact is so 

 will have to be experimentally determined, that sap- 

 rolegnia is capable of living under the same conditions. 



