BACTERIA PRODUCING YELLOW COLOURING MATTKK 109 



chemical nature being merely referred to here for the purpose of differentiation. 

 According to the researches of H. BURSTERT and F. J. HERZ (I.), a number of 

 rhodanate (thiocyanate) compounds develop in ripening curd, and when the ripe 

 cheese is cut the iron compounds therein oxidise and combine with the thio- 

 cyanates, the resulting ferric thiocyanate being in sufficient quantity to impart 

 a red or reddish tinge to the cut surface. A sample of cheese thus reddened is 

 decolorised by immersion in a solution of oxalic acid, so that this reagent should 

 be employed in doubtful cases. If, on the other hand, micro-organisms are at 

 work, the result is different. This disagreeable phenomenon is more rarely 

 encountered in hard than in soft cheeses. Red spots gradually form on the 

 surface and spread by degrees, but do not penetrate more than a few millimetres 

 into the substance of the cheese. The spots may be composed of red Eumycetes 

 or of pigment bacteria. ABAMETZ (III.) isolated two species of micrococcus from 

 red cheese, both of which develop a red colouring matter in milk and cheese ; but 

 more frequently Eumycetes, i.e. higher fungi, are the cause of this phenomenon in 

 cheese. These will be discussed in a subsequent section. 



The cause of the reddening of dried codfish (stock-fish) was investigated by 

 LE DANTEC (I.). About one-third of this article put on the market is said to be 

 affected by this evil, and is thereby rendered unsaleable, not only by reason of 

 its salmon colour, but also because of a popular belief that reddened stock-fish is 

 poisonous. The annual loss thus entailed is estimated at ten millions of francs 

 (^400,000). Le Dantec isolated three organisms from such spoiled fish ; the first 

 being a sporogenic red-producing bacillus, morphologically similar to tetanus 

 bacillus, and liquefying gelatin ; secondly, a coccus of 3-5 /j. diameter, developing 

 on gelatin to solid red colonies, but not producing a red colouring matter in 

 the fish unless accompanied by a second species of coccus, which, by itself, is 

 incapable of developing colouring matter. In order to render the reddened fish 

 fit for sale again, it is brushed in cold water and re-dried. In America borax is 

 added to the salt used in curing the fish, in order to prevent the development of 

 the evil; and an addition of from 10 to 15 per cent, of sodium bisulphite or 

 potassium nitrate (saltpetre) is also said to be efficacious. 



90. Bacteria Producing- Yellow Colouring- Matters. 



These were first studied by C. J. FUCHS (I.) in 1841, the starting-point of 

 his researches being the so-called yellow milk, i.e. milk that on standing develops 

 a pale- to orange- yellow coloration. 



The cause of this appearance was traced to a microbe named Vibrio 

 synxanthus by Ch. Ehrenberg, and afterwards known also as Vibrio xanthogenus 

 and Bacterium synxanthum. The same phenomenon was also investigated by 

 J. SCHROETER (I.) in 1870; according to whom it occurs in boiled milk only, 

 inoculations from a slightly yellowed milk into normal unboiled milk being 

 unsuccessful. The activity of lactic acid bacteria was presumably the cause of 

 this prevention. On inoculation with this microbe, boiled milk coagulated after 

 twenty-four hours, and the yellow coloration made its appearance after the lapse 

 of a second period of equal duration. Thereafter the precipitated coagulum 

 gradually disappeared and became re-dissolved, so that in six days the milk had 

 become converted into a citron-yellow, watery, strongly alkaline liquid containing 

 merely a few particles of casein in suspension. The pigment is insoluble in 

 alcohol or ether, but soluble in water ; it is unchanged by alkalies, but acids 

 combine with it to form a colourless compound. The absorption spectrum is 

 devoid of characteristic bands, and merely exhibits a darkening of the rays on 

 either side of the yellow. Schroeter proposed the name of Bacterium xanthinum 

 for the microbe investigated by him, which designation was converted in later 



