The abrasive was dipped into a suspension of 

 the bacterium before each fish was scarified. 

 Three different sites were abraded during the 

 first week. Two additional sites were abraded 

 during the second week, but because of fear of 

 mortality from trauma the severity was re- 

 duced the next 3 weeks, and the earlier lesions 

 were simply rubbed with bacterium -laden gauze. 

 Even this appeared to be severe, and during the 

 sixth to the ninth weeks inclusive, water was 

 merely drawn down three times a week and 

 charged with the bacterium . New abrasions 

 were created in the 10th and 12th weeks, follow- 

 ed by mere addition of the bacterium to the 

 lowered water during the final 3 weeks . These 

 procedures were carried out for 102 days, after 

 which some fish were held for additional 

 observation . 



By definition, kidney disease was con- 

 sidered to have been transmitted if the orgarlism 

 was presumptively identified by its morphology 

 and staining characteristic in gram -stained 

 smears of kidney or liver . It was considered 

 to be the cause of death only if many cells of 

 the bacterium were observed in most fields 

 viewed under oil immersion. After the first 

 mortality judged to be due to kidney disease, 

 sample fish were periodically taken from all 

 troughs, killed; and examined by staining smears 

 of kidney and liver . 



Results 



About 60 days after the experiment be- 

 gan, several fish in the two troughs receiving 

 the east ern st rain of the bacterium in their food 

 had symptoms of an external fungus infection 

 (probably Saprolegnia sp.). All troughs of fish 

 were treated with malachite green for 4 days, 

 and the fungus infection was controlled. This 

 was the only known occurrence of a confounding 

 infection . 



Kidney disease was not found in any of 

 the control fish, and there was good agreement 

 in the results obtained from the replicates. 



The eastern strain proved to be the more 

 virulent and was readily transmitted by abrasion. 

 It caused the first mortality among manually 

 abraded fish at 48 days. All fish so treated 

 were dead by the 102d day. Most of them died 

 of kidney disease, but some may have died pri- 

 marily from trauma . Fish subjected to conditions 

 of self-abrasion did not begin to die until the 

 96th day, and the mortality continued at a low 

 rate until the 288th day. Fish which remained 

 were killed and examined but the kidney disease 

 bacterium was not found. 



The western strain established but few 

 infections as determined by the methods used, 

 and in only one fish was it considered to be the 

 cause of death. Of the fish subjected to self- 

 abrasion, only three died; one on the 211th day 

 and two on the 296th day. The bacterium was 

 also identified in one of the fish sampled during 

 the 102 -day period. One trough of the group 

 manually abraded with the western strain was 

 lost due to an accident on the 68th day, but the 

 bacterium was presumptively identified in only 

 one fish. Most of the fish in the other trough 

 which had been manually abraded (15 fish) sur- 

 vived to the 296th day, but when killed, none was 

 found to harbor the bacterium . All but the three 

 mortalities in the self -abraded fish which re- 

 mained after sampUng survived to the 296th day: 

 the kidney-disease bacterium was not identified 

 in any of the fish killed at termination. 



Discussion 



Although none of the methods used re- 

 sulted in establishing uniform infections in the 

 groups on which it was tried, much useful informa- 

 tion was obtained. 



Clearcut differences were noted in the 

 results obtained with the different strains of the 

 bacterium . Because such factors as host species, 

 length of time cultivation was carried out on 

 artificial medium, and the like, there is at this 

 time no importance implied to the geographic 

 origin of these strains. 



No methods of feeding achieved transmis- 

 sion, and no mortality was caused by the feed- 

 ing of bile salts or glass shards (table 1). 



In strong contrast to ulcer disease and 

 furunculosis, which are usually acute in eastern 

 brook trout, the results of this experiment em- 

 phasize the chronic nature of kidney-disease 



