DESCRIPTION OF SPECIES 



431 



on potato is blue-green or lead- 

 grey instead of brown. 



Bouillon — The liquid becomes 

 turbid, and takes a greenish-blue 

 tint ; a thick dirty white deposit 

 is formed. A pellicle is sometimes 

 produced. 



Milk — No coagulation or forma- 

 tion of acid, but with age a feeble 

 alkaline reaction is noticeable. A 

 bluish leaden coloration appears 

 on the surface in patches, then 

 extends over the whole superficial 

 layer. When the milk has been 

 sterilised, the blue tint is not im- 

 parted to the liquid, which is simply 

 greyish at the top. In ordinary 

 milk, on the contrary, the whole 

 rapidly becomes a beautiful sky- 

 blue colour on account of lactic 

 acid present. When grape sugar is 

 added to sterile milk the bacillus 

 produces a blue colour. 



Mineral solutions — Hiippe re- 

 commends, as a culture medium, 

 mineral solutions with tartrate of 

 ammonia base. W^hen one of these 

 liquids is inoculated, a diffused 

 flocculent turbidity is quickly pro- 

 duced throughout the whole. Then 

 on the surface a thin white pellicle 

 is formed, and the liquid takes a 

 bluish tint. A green coloration 

 then appears beneath the veil which 

 invades the whole of the liquid in 

 14 days ; the membrane itself 

 becomes grey-green ; it disinte- 

 grates from within, and its debris 

 form a dirty white deposit at the 

 bottom of the glass. The green 

 tint of the liquid turns later to 

 yellow, and the reaction is clearly 

 alkaline. The green can be turned 

 to blue by oxidation or by the 

 addition of a little lactic acid. In 

 simple solutions of sugar, peptone, 

 glycerine or urea, no coloration is 

 visible, but it appears when tartrate 

 of ammonia is added. This 



property of secreting pigment does 

 not appear to decrease by succes- 

 sive cultures as is the case with 

 many chromogenic species. It 

 remains as pronounced after a large 

 number of generations and in 

 very old cultures. The ' optimum 

 temperature for the formation of 

 colouring matter is from 15' to 18% 

 it is hindered at 25", and no longer 

 takes place at 37°. 



Vitality — Does not resist much 

 heat ; a temperature of 60° will kill 

 it in a few minutes. Therefore it 

 is doubtful whether the formations 

 described as spores should really 

 be considered as such. Withstands 

 desiccation for a long time. 



The pigment has not been ob- 

 tained in a pure state. It appears 

 to be slightly soluble in acidulated 

 water, insoluble in water, alcohol, 

 and ether ; it also dissolves slightly 

 in glycerine. It decomposes very 

 quickly ; solutions rapidly pale in 

 the light, a little more slowly in 

 the dark. Treated with organic 

 acids or attenuated mineral acids 

 the solution does not change colour ; 

 with ammonia it becomes violet, 

 and with potash and soda rose-red ; 

 the blue colour is restored by acids. 

 When treated with potash and left 

 for some time, from 12 to 24 hours, 

 from rose-red it becomes brick- 

 red, showing a very marked fluor- 

 escence ; the colour is not restored 

 to blue by acids, but turns yellow 

 and decolorises little by little. 

 Under the spectroscope the blue 

 solution shows a thick band of 

 absorption into the yellow, on the 

 line D of Frauenhofer. As well 

 as the characteristic blue pigment, 

 this bacillus produces another 

 colouring matter which gives to 

 the medium a greenish fluorescence. 

 Modifications of colour occur in 

 varieties of the organism. 



