166 BULLETIN OF THE UNITED STATES FISH COMMISSION. 



further growth in length was not noticed. The filaments usually reached a length of 

 a third to half an inch. In ten days or two weeks further development was usually 

 stopped by bacteria. No cultures being successful in the hygeia water, it was regarded 

 as pure and used to place the flies in after their inoculation. 



At first no cultures were obtained from water taken just before its entrance into 

 the various tanks of the aquarium, and it was thought to be free from the fungus, but 

 as more were attempted an occasional growth of Saprolegnia appeared, quite similar 

 to that found on the fish. About a third of the tests of water from this source gave 

 cultures — a proportion large enough to indicate that the water supply may have 

 been the original source of infection. The fact that cultures were thus occasionally 

 obtained from the water just before it entered the tanks was probably due to the 

 imperfect working of the filter system, which was sometimes out of order, the water 

 in the tanks then becoming quite turbid. It was said that the clearness of the water 

 was similarly affected when the lake was especially rough. When the fungus had 

 once obtained a foothold in the tanks it became, of course, much more abundant in 

 its spore forms. Cultures obtained from water from the lagoon and from the edge of 

 the lake yielded in every case some form of Saprolegniaceai. 



There was some slight difference in the number of successful cultures in water 

 taken from the various tanks. For example, growths were almost invariably obtained 

 from those tanks that contained infected fish, while water from tanks in which the fish 

 were not diseased yielded cultures in scarcely more than half the cases. 



Another difference was found in the character of the growths. While on the fish 

 themselves nothing but a species of Saprolegnia was found, in water cultures from 

 the different tanks three genera were encountered; viz., Saprolegnia., Achlya, and 

 Leptomitus. The Leptomitus was found only as a secondary product in a few impure 

 cultures that were not well developed. Pure cultures of either the Saprolegnia or 

 the Achlya were usually obtained, but occasionally a growth was found in which they 

 both occurred. Still another distinction was noted: The water cultures from aquaria 

 containing badly "fungused" fish almost invariably gave Saprolegnia — commonly a 

 pure growth ; those from aquaria in which the fish were healthy, generally gave Achlya; 

 while those from tanks in which the fish were slightly affected by the disease yielded 

 either Achlya or Saprolegnia or an impure growth of both. The Achlya and Saproleg- 

 nia cultures could be readily distinguished even with the naked eye. The former had 

 the longer filaments, and the bunch of zoospores clustered at the opening of the emptied 

 zoosporangia could easily be seen. In cultures of the Saprolegnia the filaments formed 

 a rather dense growth which radiated from the fly for about a third of an inch. When 

 the zoosporangia began to form, the threads became more opaque at their free ends. 



The tests of water taken from the tanks at various depths gave us no differential 

 results. It seemed to make no essential difference in the character of the growths 

 whether the water came from the top, the center, or the bottom of a tank. 



Numerous experiments were made by placing a little of the fungus taken from 

 diseased fish on flies in hygeia water. These cultures were always successful, and, 

 so far as one could judge from the asexual stage, were of the same species as those 

 obtained from the water cultures which gave growths of Saprolegnia. 



Altogether, something over 100 cultures with flies were made, but in none of 

 those which yielded the Saprolegnia, and in none of the numerous specimens examined 



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