BLUE COLORATION OF MILK. 151 



Bacillus lactis cyanogenus is therefore chromoparous. The con- 

 stitution of the colouring matter has not yet been determined 

 with accuracy, but 0. ERDMANN (I.) was led by his comparative 

 experiments to consider it as one of the aniline group, viz., 

 triphenylrosaniline. Neelsen's endeavours to prepare it in a pure 

 condition were frustrated by reason of its instability. Dilute 

 solutions of acetic acid, hydrochloric acid, phosphoric acid, sul- 

 phuric acid or nitric acid produce no noticeable alteration. Am- 

 monia gives rise to a violet tint, whilst under the influence of 

 the hydroxide or the carbonate of potassium or sodium, conversion 

 into a beautiful rose-red occurs, the original colour being restored 

 by acidification. Frequently the low degree of acidity of the 

 milk, under which condition the bacillus is still able to develop, 

 is insufficient to enable the colouring matter to assume a deep blue 

 tint. The colour of the surface of the liquid is merely greyish- 

 blue, and only becomes a pure, full blue when the lactic acid bacteria 

 come into action and raise the acidity to a sufficient degree. The 

 colour shade in individual instances may exhibit any intermediate 

 tint between a delicate light blue and the deepest indigo. Accord- 

 ing to Neelsen, the absorption spectrum of this colouring matter, 

 which consists of the strong lines E and F and of a broad band in 

 the yellow, is almost identical with that of triphenylrosaniline. 

 From the researches of C. GESSARD (I.) and K. THUMM (I.), it 

 appears that Bacillus cyanogenus also produces, in addition to the 

 blue colouring matter, a yellow fluorescent substance. L. HEIM 

 (III.) and P. BEHR (I.) have given an account of a variety of this 

 bacillus that had lost its faculty of producing colouring matter in 

 nutrient gelatin, nutrient agar-agar, and skim milk. W. ZANGE- 

 MEISTER (I.) found on milk that turned blue spontaneously a 

 fission fungus (B. cyaneo-fluorescens) allied to Bacillus cyanogenus, 

 further particulars of the properties of which will be found in the 

 treatise referred to. 



Bacillus cyanogenus is not injurious to health. The poisonous 

 properties attributed to blue milk by early observers Steinhof 

 and Hosier have been controverted by Haubner; therefore, if 

 illness has actually ensued on the consumption of such milk, the 

 fission fungus in question was not to blame. Harmlessness apart, 

 blue milk is not a merchantable article, and its sale should be 

 prohibited, since its appearance is, to put it mildly, unappetising. 



Since the causes of this blue coloration in milk have become 

 known, its occurrence has, as a rule, been very limited ; and when 

 it is observed, many ways of combating it are employed, chief 

 among them being scrupulous cleanliness in all appliances and 

 utensils with which the milk comes into contact. The dairy or 

 milk -room is then thoroughly sulphured several times, and, 

 finally, a little salt or Glauber salt (sodium sulphate) is added 

 to the cows' dietary. This last-named remedy must, however, 

 be employed with discretion, since, under certain circumstances, 



