short the survival time of B» saljnonicida, thus being from the organism 

 point of view an inhibitor of epizootic spread of disease. Again^ 

 organic or inorganic pollution could lovrer the resistance of fish in a 

 river or stream to such a degree that almost regardless of its effect 

 on the number of B. salmonicida present, an epizootic would develop. 

 This seems to the author the wisest stand to take on the question of 

 pollution in relation to f urunculosis , 



Lack of oxygen 



Since in nature^ deaths from furunculosis frequently take place 

 among fish which are collected in pools where they may have insufficient 

 oxygen^ the Furunculosis Committee (1933) attempted to simulate this 

 environmental condition in experiments, 1^ keeping water temperature 

 I0W5 deprivation of oxygen per se could be testedo 



Ten yearling brown troutp exposed to infection some months before, 

 were kept in still water for several days. Two died in 3 days and two 

 in 4 days, and one of each pair was found to have B. salmonicida in the 

 kidney. The remaining six fish were in great distress on the sixth 

 day and were killed^ the kidneys of two yielded cultures of B. 

 salmonicida . This result suggests that yearling trout which are harboring 

 a latent infection in their kidneys are no more liable to die when the 

 oxygen content of water is diminished than are healt!:^ fish (Furunculosis 

 Committee 1933). 



Ten 2-year-old brown trout were exposed to infection ty contact 

 with an inoculated fish and survived for 28 days. The supply of water 

 to the tank was then shut off, and in 24 hours two fish were dead. B. 

 salmonicida was isolated from the heart, blood, and kidneys of both. 

 In 4-8 hours the remaining eight fish died, and one of these proved to 

 be infected. In this experiment iivith 2-year-old trout, the Furunculosis 

 Committee (1933) concluded that fish in which the disease had reached 

 the bacteremic stage were less able to withstand decrease in oxygen. 



Other factors 



The question arose to the Furunculosis Committee (1933) as to 

 whether or not the spread and development of the disease is influenced 

 by the hydrogen-ion concentration of water. Observations of the disease 

 in various natural waters, including peaty waters and hard water 

 streams, have not suggested that the type of water influences the 

 development of the disease (Blake and Clark 1931). An attempt was made 

 by experimental methods to ascertain whether or not water to which peat 

 moss had been added in one case and chalk in the other affected the 

 development of furunculosis in trout as compared with or-dinary tap 

 water. It was found that B. salmonicida did not retain its viability 

 as long in peaty water (having a pH of 6.6) as in tap water and water 

 containing chalk, but infection could be set up in trout kept in each 

 type of water when culture was added to the tank. 



4S 



