96 THE SAPROLEGNIACE^ OF THE UNITED STATES, 



One or more species of the group are facultative parasites which can attack liv- 

 ing fishes and Amphibia, and cause serious disease which usually results in death. 

 Under certain conditions which are not yet well determined, the disease may b:>come 

 epizootic and cause great mortality in a lake or stream or in some restricted part of 

 it. Notices of such cases occur throughout the literature fi-om the time of Hannover 

 ('39) and linger ('43) to the present. The most famous outbreak, and the one best 

 studied, was that on salmon and some related fishes in the rivers Esk, Eden, ISTith, 

 and others in England and Scotland. The details concerning this attack and con- 

 cerning the pathology of the disease may be found in the papers of Smith ('78), Stir- 

 ling ('78, '79, '79 a), Brook ('79), Buckland ('80), and Huxley ('82). It is sufficient 

 to say here that Huxley was convinced that the disease was caused by a truly para- 

 sitic Saprolegnia, called by all writers on the disease, 8.ferax. The only reference to 

 the occurrence of a similar epizootic in America which has come to my notice, is a 

 brief note by Gerard ('78), who reported severe mortality among fishes, from this 

 cause, in the Passaic river in ]^ew Jersey. 



Murray ('85) and Schnetzler ('fc7) have found that the zoospores of "/S. ferax''"' 

 cultivated on flies can attack living fishes and frog-tadpoles and produce a growth of 

 the fungus which kills the victim. Some facts concerning the effects of ^. racemosa 

 in a fish-hatchery will be discussed in connection with the description of that species. 



Owing to the absence of suitable substrata for their development in mass, and 

 the brief time required for the completion of their life-cycle, these plants are not often 

 found growing spontaneously; and this fact has led to the belief that they are some- 

 what rare or difficult to obtain. But the writer's experience in the United States 

 fully agrees with that of DeBaiy in Europe that this is by no means the case. The 

 last-named author has given ('88) very practical hints for obtaining and cultivating 

 them which it will not be superfluous to repeat here, with some additions drawn from 

 personal experience. For reasons above stated, the most prolific source of supply is 

 water containing green Algse, and the best substi'atum is afibrded by insects such as 

 common house-flies or meal-worms. For material, a handful of Algae may be taken 

 from the stream, pond, or pool in which they are growing and placed in a collecting 

 bottle or other vessel which will protect them from drying. In the laboratory, these 

 are placed in a vessel of water from the public or private water supply, and the cul- 

 tuie insects are thrown upon its surface. The collection of a mass of Algse without 

 water, except that retained by the mass, reduces the bulk of specimens, which is of 

 importance when they are taken at a distance from the laboratory, and largely excludes 

 aquatic organisms which might make trouble in the cultures; while experience shows 



