472 Bacterial Disease of Pisum sativum 



the incubator. This pinkish colour cannot be due to acid, as all the 

 blue coloration of the reduced litmus has disappeared. The colour 

 then changes from apricot to deep sherry, and finally the liquid is a 

 clear, deep wine shade with a heavy bacterial sediment. The action 

 on litmus milk is slow. 



Glycerine. There is good growth on glycerine without the formation 

 of gas or acid. 



Nitrate reduction. Nitrate is reduced to nitrite without the formation 

 of gas. The organism soon loses its power of reducing nitrates when 

 grown on artificial media. Only young cultures from the growing 

 stem and freshly incubated cultures from the dry cotyledon should be 

 used for this test. The organism however retains its power of reducing 

 litmus a very much longer time. The apricot reaction occurs with 

 cultures some months old. The nitrite test used was that recommended 

 by Jordan (8), namely: 



After four days incubation in nitrate broth (0-1 per cent, peptone, 

 0-02 per cent, nitrite-free potassium nitrate) add to 3 c.c. of the culture 

 2 c.c. of each of the following: 



(1) Sulphanilic acid solution made by dissolving 8 grammes of the 

 purest sulphanilic acid to 1000 c.c. of 5N acetic acid (sp. gr. 1-041). 



(2) a-Amidonaphthalene acetate solution prepared by dissolving 

 5 grammes solid a-Naphthylamine in 1000 c.c. of 5N acetic acid and 

 filtering through absorbent cotton wool. 



The development of a rose colour indicates the presence of nitrites. 



Diastatic action. The organism has no diastatic action on pea starch. 



Stah Cultures. The line of puncture is indefinitely beaded and growth 

 occurs down to the bottom of a closed agar stab. 



Reactions to stains. In the rod stage Ps. seminuni takes the 

 usual bacterial stains very readily. It is gram-positive and non-acid- 

 fast. But as already stated above the oval bodies only stain lightly. 

 The flagellae are also very difficult to stain ; the best results were 

 obtained with van Ermengen's flagella stain. 



Isolation of the organism. The organism has been isolated from the 

 centre of both green and dry cotyledons, from the stem, from the pod, 

 and from the hair-like outgrowths sometimes found lining the pod. 



Motility. Whjen the parent rod is about to divide, it has a slow 

 sinuous motion, but when division is completed, the daughter rods 

 have been seen at first to revolve very rapidly on their own axes, as 

 indicated by the arrows in Plate VII, fig. 14 a, and then to dart about 

 the field of the microscope. When observed alive in the cells of the 



