140 CHROMOPAROUS BACTERIA. 



colonies on the nutrient media referred to resemble in appearance 

 those of the first-named species. In addition to liporhodine, how- 

 ever, it produces a yellow colouring matter, soluble in water, but 

 of unknown nature. 



Antithetical to these two red-producing species are : Bacterium 

 egregium, obtained from atmospheric dust ; then Bacterium Chryso- 

 gloia ; and finally the Staphylococcus pyogenes aureus already 

 several times referred to in the previous chapter. These three 

 develop into yellow cultures producing lipoxanthine, the absorption 

 spectrum of which consists of two bands, one near F and the 

 other between F and G. 



89. Red Coloration in Milk 



may be due to various causes, one of them being an admixture of 

 blood derived from a broken blood-vessel in the udder. In this 

 case the coloration of the liquid is not uniform, but is due to 

 scattered patches of red, flocculent blood coagulum. If, on the 

 other hand, the milk is found to be uniformly coloured red or 

 reddish throughout the entire mass as soon as it is drawn from 

 the udder, then other causes are in operation. If the colour 

 undergoes no change on standing, it is attributable to the fodder 

 having contained a large quantity of madder (Rubia tindorum) or 

 of Galium verum. Should, however, the red-drawn milk pre- 

 cipitate a red sediment on standing, the colour of the liquid con- 

 currently decreasing, then the coloration is due to a transudation 

 of haematin. This case is analogous to that of " red water," and 

 is a consequence of the consumption of highly stimulating fodder. 



When, however, a normal milk gradually becomes red after 

 standing, then micro-organisms are at work (Micrococcus prodigiosus 

 being frequently the agent), and the colouring matter excreted by 

 the organism is absorbed by the fat globules of the milk. This 

 microbe has already been more minutely characterised in the 

 preceding paragraph. 



A second milk -reddening organism is the Bacillus lactis 

 erythrogenes, discovered by Hueppe and more closely examined 

 by GROTENFELT (I.). The non-motile rods of this organism are 

 0.3-0.5 p in diameter, with, usually, a length of 1-1.5 f** DU * 

 attaining to 4.3 p in bouillon. This fission fungus (which liquefies 

 gelatin) grows on solid media to yellow colonies which excrete 

 around their periphery a red colouring matter. When inoculated 

 into sterile milk it produces a gradual coagulation attended with 

 a sickly-sweet odour, without affecting the reaction of the liquid 

 to any appreciable extent. The serum, gradually clarifying from 

 the deposited casein absorbs the resulting deep red colouring 

 matter, which develops most copiously in the dark and ceases to 

 form if the culture be exposed to light or the medium has an acid 

 reaction. Its absorption spectrum exhibits two strong bands 



