Potato 



At no time is growth profuse on potato (Marsh 1903, Arkwright 

 1912., Mettam 191^? Williamson 1928), Duff and Stewart (1933) found a 

 scant,, creamy, raised filiform growth in about 5 days which later became 

 a dirty grayish color, Stevens and Keil (1931) claimed a slight growth 

 occurred after 4.8 hours and pigment after the third day. 



Pigment production 



Several authors ha-ye studied the brown pigment produced by B. 

 salmonicida in culture as this is one of the chief characters by which 

 the organism may be identified, Clxromogenesis has been found to occ\ir 

 only under aerobic conditions (Williamson 1928, Duff and Stewart 1933). 



It has been found that a slight acidity of media tends to inhibit 

 pigment production (Plehn 1911^, Williamson 1928 )» Williamson (1928) 

 showed that when the pH was less than 7,6 chromogenesis was proportionally 

 less. Similarly, Marsh (1903) found that pigment production was inhibited 

 in extremes of reaction but did occur in alkaline, neutral and acid media. 



The optimdm tsmperatiare for chjcmogenesis is the optimum for 

 growth (Furunculosis Committee 1930), Marsh (1903) stated that higher 

 temperatures inhibited pigment production faster than growth of the 

 organism. 



Williamson (1928) found chromogenesis to be at a maximum on solid 

 media, appearing on fluid media after a longer time. It occurred in 1 

 to 2 months in liquefied gelatin (Williamson 1928). In broth, pigment 

 has been reported after 3 days to 2 months (Stevens and Keil 1931, 

 Williamson 1928), Marsh (1903) claimed that no pigment formed on gelatin 

 but Plehn (1911) found it after the second week. 



The intensity of pigment produced by different strains of the 

 organism is variable (Duff and Stewart 1933), Occasionally after prolonged 

 subculture a strain may lose its ability to produce pigment on agar only 

 to regain this property after further subculture or following a change 

 to serum medium, Arkwright (1912) found that pigment may not be formed 

 on primary isolation of the organism but would show up on subculture. 

 Again, sometimes he noted that plates which were crowded with almost pure 

 cultures of B. salmonicida remained without pigment for 5 days or more. 



Growth but jAck of pigment production does not necessarily 

 indicate that B, salmonieida is absent. This is due to the fact that 

 various factors (pH, temperature, nature of media, and strain of 

 organism) may determi)ie the time of appearance, and even the presence 

 or absence,, of pigmentation. 



12 



