BLUE MILK 173 



These conditions appear to be : — 



1. An association of other organisms — the lactic acid producing 

 bacteria. 



2. The production of acid set free by these organisms in such 

 proportion as to be readily taken up by the Bacillus cyanogenes as 

 soon as formed, so that it never exists in excess. 



The addition to sterile milk of lactic acid per se will not, in 

 conjunction with the micro-organism, give rise to the coloration, 

 and to make it appear under these conditions it is necessary to 

 add to the milk some natural substance {e.g. glucose), of which the 

 organisms can make use in producing such an amount of acid as 

 is necessary for their existence and development, for alone they 

 have not the power of reducing milk sugar to lactic acid. They 

 ferment glucose with production of acid, the blue colour in this 

 case being produced. The milk infected with the disease transmits 

 its colouring properties to butter prepared from it. 



Introduced into ordinary milk the organism produces no 

 coagulation, and the reaction becomes fully alkaline ; a bluish 

 coloration appears on the surface at first in patches, which gradually 

 extend themselves over the whole surface. The milk serum, how- 

 ever, rarely becomes affected. Grotenfeld states that its ordinary 

 growth in milk favours the multiplication of many common milk 

 organisms which in their turn destroy B. cyanogenes. 



In sterile milk little or no blue tint is apparent ; the upper 

 surface, however, at times takes a greyish hue if the reaction is acid. 



Cultures of the organism made in mineral media are very 

 characteristic ; the medium quickly becomes turbid, and a thin 

 white veil appears on the surface, the medium itself taking a bluish 

 colour. Later a green tint appears, and this gradually extends until 

 after some twelve or fourteen days the whole of the liquid becomes 

 coloured, the veil itself turning a greenish-grey. In older cultures 

 the greenish tint of the liquid turns to yellow, and the reaction is 

 strongly alkaline. 



In saccharine solutions or glycerinated media the blue colour is 

 rarely, if ever, present. The best temperature for the formation of 

 colouring matter would appear to be from 15" to 18° C. ; it is 

 difficult to obtain at 25', and at 37" loses the property entirely. 



A temperature of 60" C. for some minutes would appear 

 entirely to destroy the activity of the organism, but it stands 

 desiccation for a lengthened period.^ It is not pathogenic. 



^ According to Heim this period does not extend beyond five or sevea 

 months. 



