( 160 ) 
Here likewise the culture is effected at 25°. 
With observation of the said proportion and operating as described 
under B. stutzeri, the different varieties of B. vulpinus can also be 
obtained from canal water. 
The denitrification sets in very slowly and the development of gas 
gets not by far the intensity perceived in the preceding species. 
Here, too, by the complete disappearance of all liquefying bacteria 
already at the first transport, the isolation of the wished for species 
is much facilitated. Although at sowing the crude cultures on broth 
gelatin some B. vulpinus colonies may already be perceived, they 
multiply so much in the transports, that plates therewith prepared, 
appear, so to say, quite covered with the large, flatly spread, trans- 
parent, fox-coloured colonies of this species. 
If for the accumulation other organic salts than tartrate are used, 
or a higher rate of nitrate than 0.2°/,, not a single colony of B. 
vulpinus is detected, though it was certainly present in the infection 
material as it is universally, distributed in the soil. 
By their growth the colonies strongly remind of the flatly spread 
variety of B. fluorescens non liquefaciens, but of fluorescence nothing 
is seen. In shape and motility the bacterium corresponds with 
B. stutzeri. 
An interesting property of B. vulpinus is, that the brown pigment 
only develops under the influence of light. If simultaneously two 
cultures of this species are made on broth gelatin, and one, wrapped 
in black paper, is put in the dark, and the other in the light, for 
the rest in equal conditions, a great difference is perceptible. This 
becomes more obvious still, when making reinoculations or transports 
of either culture, likewise keeping these respectively in the dark and 
the light. So-doing a perfectly colourless culture can be obtained, 
but if this is again inoculated in the light, the brown colour returns. 
The pigment formation only takes place at growth, so that colonies, 
full-grown in the dark do not colour when exposed to light. 
B. vulpinus belongs to the group of real chromophores *), i.e. the 
pigment is bound to the bacterial body, and the behaviour towards 
light is, in my opinion, another indication that in this group the 
pigment „has a biological function. 
The auxanographic examination proved, that with nitrate for nitrogen 
nutrition, a feeble growth is obtained with kalium-malonate, a 
vigorous one with levulose, glucose, maltose, kalium-citrate, succinate 
') See Beuertvcx, La biologie d'une bactérie pigmentaire. Arch. Néerl. 1892, 
T. 25, p. 227. 
