.142 CHROMOPAROUS BACTERIA. 



-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 un- 

 successful. 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 gradu- 

 ally 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 sus- 

 pension. The pigment is insoluble in alcoholor ether, but soluble 

 in water ; it is unchanged by alkalies, but acids combine with it 

 to form a colourless compound. The absorption spectrum is de- 

 void of characteristic bands and merely exhibits a darkening of 

 the rays on either side of the yellow. Scbroeter proposed the 

 name of Bacterium xanthinum for the microbe investigated by 

 him, which designation was converted in later text-books to 

 Bacillus synxanthus. It is desirable that the study of the organ- 

 isms of yellow milk should be taken up anew, since Schroeter's 

 investigations were not performed upon pure cultures in the present 

 acceptance of the term. 



With the species hitherto described (Bacterium egregium, B. 

 Chrysogloia, Staphylococcus pyogenes aureus, B. synxanthum} there 

 can be associated a number of others, equally characterised by the 

 faculty of producing yellow colouring matters. Of these, mention 

 will here be made merely of the Micrococcus ochroleucus, discovered 

 by 0. PROVE (I.) in human urine in a state of incipient decomposi- 

 tion. When kept in the dark this microbe develops into colourless 

 cultures, but if exposed to diffuse daylight or the sun's rays, it 

 elaborates a sulphur-yellow colouring matter. This may, therefore, 

 be regarded as a probable means of protection. 



