Differentiation of Certain Genera of Gram Negative Baeteria 511 



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Fig. 5. Gut group Vibrio (39) showing curved rods and the characteristic 

 round bodies. Phase Contrast X1200. 



These include Pseiidomonas ichthyodermis (27) and Achromo- 

 bacter ichthyodermis (58, 60). 



Previously it has always been difficult to differentiate the 

 saprophytic vibrios causing disease in poikilothermic animals 

 from other Gram negative polar flagellate rods. This was usually 

 done on the basis of the curvature of the cell, quite an unsatis- 

 factory criterion. The femientative character of their attack on 

 carbohydrates, together with their sensitivit}' to tlie pteridine 

 compound (0, 129) are thus \aluablc additional criteria. In addi- 

 tion to the curvature of the cell, Vibrio comma was characterised 

 by early workers by the pleomorphism of the cell and in particular 

 by the presence of round or coccoid bodies ( 24, 26 ) . Hallock ( 22, 

 23) has recently claimed that this is a distinguishing feature of 

 the Vibrio group as a whole and more attention might be given to 



