8. G. Paine 487 



organism producing lively rotting of the potato. Whereas the impure 

 cultures had always given from the first a pinkish-brown colour in the 

 rotted tissue or a mixture of brown, black and yellow, the rot produced 

 by the pure culture was not coloured at all until about a week after 

 inoculation, when a slight pink tinge developed in the rotted part 

 bordered by a brown stain in the surrotinding tissue which finally turned 

 almost jet black. 



After two transfers to fresh sterile potato slices the organism was 

 plated out on bouillon-gelatine and incubated at 19° C. On the second 

 day thirteen colonies all apparently similar had made their appearance 

 and had produced a basin-shaped liquefaction of the gelatine with a dia- 

 meter of four to five millimetres. Each of the thirteen colonies was 

 inoculated upon potato tissue and gave rise to the rot characteristic 

 of the organism as described above. This was taken as proof of the 

 purity of the culture and examination of the organism in stained 

 preparations and under "dark-ground" illumination further verified this. 



DESCRIPTION OF THE ORGANISM. 



I. Morphological Characters. 



Form and Size. The organism is a short rod with rounded ends. 

 When taken from the diseased tissue after 48 hours incubation at 

 20° C. the length of the single rod varies from l-2yLt to 2-4/z and the 

 breadth from 0-7/x to 0-8 fi; pairs of organisms are very numerous and 

 measure up to 3-5 ;li in length. Taken from bouillon-agar the length 

 of the rods is more variable and pairs of organisms are riot of such 

 frequent occurrence but the organism has a tendency to form in chains. 

 The measurements were made upon preparations fixed five minutes in 

 4 per cent, formahn, stained 10 minutes in aqueous methyl violet and 

 examined in oil. 



Motility and Flagella. The organism is an actively motile bacillus 

 and swims with a rapid rotation on its long axis. The flagella are 

 peritrichous and three to six in number when taken from an agar 

 slope, but many are uni-flagellate when taken directly from diseased 

 tissue. Beautiful stained preparations of the flagella were obtained by 

 a modification^ of van Ermengen's method and also by Lowit's method. 



1 This was a modification by Stevens and I am indebted to Dr R. S. Williams for 

 having introduced it to my notice. Details of the method are given in Hewlett's 

 Bacteriology, 5th Edition, 1914, page 115. 



