470 Bacterial Disease of Pisum sativum 



(3) Radiating semi-opaque colonies. 



(4) Submerged colonies, flat disks with roundish lenses in the 

 periphery (Plate VII, fig. 12). 



This plate to all external appearances looked impure, but careful 

 tests of all these four types of colonies gave identical and typical 

 reactions with litmus milk. A good deal also depends upon the morpho- 

 logical stage of the organism at the time of plating. Replatings from 

 one solid medium to another tend to retain their original colony 

 characteristics, but ringing the changes between solid and liquid media 

 only led to further puzzling results and occasional impurities. 



The inference to be drawn from these facts is that there are possibly 

 two strains of Ps. seminum which differ only in their shape of 

 colony. One strain may be more capable of complete division than the 

 other. The proportion of definite rods to oval bodies is greater in the 

 radiating colonies than in the circular surface colonies. 



Platings from young cultures and from very old cultures in liquid 

 nutrient media, give much more uniform results than platings from the 

 intermediate stages. Also platings of the pellicle are naturally much 

 more varied than when the pellicle is avoided and platings made from 

 the broth itself. The colonies also vary in general characteristics 

 according whether the medium is acid, alkaline, or neutral (Plate V, 

 figs. 3, 4, 5) although the organism grows well on all three. Plate V, 

 figs. 3 and 4 show magnifications of giant colonies of the same culture 

 on neutral and alkaline media, and it will be seen that on neutral pea 

 agar agar the individual submerged colonies are much more definitely 

 lens-shaped than on the alkaline medium. 



Plate V, fig. 5 also shows the different growths although the platings 

 are rather thick, and Plate VII, fig. 12, drawings of varying shapes in 

 submerged colonies, all of which give the typical litmus milk reactions. 



Biochemical Reactions. 



Ps. seniiniDii is a facultative anaerobe and will grow to the bottom 

 of a closed agar stab. 



Beef broth. The organism grows well on acid (1 per cent, normal 

 HCl), neutral and alkahne (1 per cent, normal NaOH) broth. A pellicle 

 is formed, which, on shaking, sinks to the bottom of the liquid and 

 forms a stringy precipitate. This precipitate gradually disappears and 

 the liquid becomes turbid. Both oval bodies and rods strung together 

 in long chains occur in the pellicle, but if the latter is avoided, rods and 



