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the fact that such outbreaks have, at least on several occasions, synchronised in 

 the two localities, and that weather conditions have been more or less similar, is 

 stronj^ evidence in favour of assuming that the organisms concerned in the two 

 cases" are specifically identical. It must be pointed out, however, that in the 

 Brisbane River outbreak, all the diseased fish examined were estuarine. and 

 that we did not know in what locality infection occurred. It must have been 

 many miles up stream, as the river during winter is distinctly salty (the rainfall 

 being a summer one), and therefore probably more or less alkaline where the 

 diseased fish were collected, but higher up stream, beyond the reach of the tide, 

 conditions would be different. Though the diseased fish were estuarine. the 

 organisms obtained from them caused a similar disease when introduced into a 

 fresh water fish, e.g., goldfish. The causal organism appears to us to be new to 

 science, consequently we have designated it Bacillus piscivorus. 



Hofer (1906) gave a short account of several bacterial diseases of fresh 

 water fish, including Salmonidae, but the Brisbane organism is readily separable 

 from all those referred to by him excepting Bacterium saluwnis-pcstis, Paterson 

 (1903), the cause of the well-known salmon disease (Drew, 1909). The latter 

 is an actively motile, non-sporing, gram-negative, short, thick bacillus or diplo- 

 bacillus which liquefies gelatin and coagulates milk with a slow acid reaction. 

 It is pathogenic for fish, especially the Salmonidae. It thus differs from B. 

 piscivorus in its reactions towards milk and gelatin. 



Another organism to be considered is B. truttae, Marsh (1903), which 

 causes an epidemic amongst American Salmonidae. It is a gram-positive, non- 

 motile, short bacillus, or diplobacillus, which grows best at a titre ranging from 

 neutral to +05 acid to phenolphthalein, and at the latter titre Avill liquefy gelatin, 

 though not at a titre of +15 when growth becomes practically inhibited. It 

 liquefies blood serum ; does not clot milk but peptonises it, and the reaction is 

 neutral or faintly acid. In bouillon cultures (+05) after eighteen hours there 

 is no clouding but there is sedimentation; while after 10 to 15 days a char- 

 acteristic brown colour appears in the medium and the sediment becomes dirty 

 brown, changing with age to dark brown. The colonies on agar change from 

 greyish-white to greyish-brown on and after the third day. The Brisbane 

 bacterium differs from B. truttae in its reaction to gram, its growth on agar 

 (the former growing well on +15 agar, as well as on +0'5), absence of pig- 

 mentation in old colonies, distinct clouding of bouillon in 18 hours but no appear- 

 ance of a brown colour even after four weeks at room temperature (20°-22" C), 

 effect on gelatin and blood serum as well as on milk. Moreover. B. truttae is 

 reported to be killed by exposure to a temperature of Z7° C. for 17 hours, 

 whereas B. piscivorus is not. 



The cultural reactions of the Australian organism resemble those of Bacillus 

 fecalis-alkaligeues in regard to growth in bouillon and gelatin, the non-fermenta- 

 tion of all sugars and gram staining. The latter is very actively motile and an 

 alkaline reaction is marked on the first day of growth in litmus milk. The 

 fermentation reactions and the active motility readily distinguish B. piscivorus 

 from B. typJiosus and its allies. 



Two bacterial organisms have already been described from Australian marine 

 fish by Grieg Smith (1900), vie, B. piscicidus bipolaris and Vibrio bresijiiae. 

 The former liquefies gelatin, coagulates milk, is actively motile, forms spores, 

 and is gram positive; while the latter liquefies gelatin, turns litmus milk acid, 

 bleaching it in seven davs, and gives a slight indol reaction after seven days' 

 growth in bouillon. 



If Castellani and Chalmers' (1919) classification of bacteria be accepted, 

 then the name Alcaligenes piscivorus should be applied to the new organism, as 

 its reactions place it in their genus Alcaligenes, near B. fecalis. 



