154 CHROMOPAKOUS BACTERIA. 



tion of 0.5 per cent, of peptone in ditch-water they only develop 

 to 0.3-0.6 ft by 0.15 ju,. If we follow up the alterations gradually 

 occurring in a culture of this fission fungus in the latter medium 

 at 10 C., we find that after four or five days the liquid, which 

 has hitherto been pale yellow, assumes a more and more decided 

 greenish cast. A sample taken from the bacterial skin covering 

 the surface discloses two constituents : a number of colourless 

 rods connected to form bands, and, secondly, lying between them, 

 the blue pigment granules, almost globular in form and 1.5-3.5 /* 

 in diameter. The colour of the liquid then successively changes 

 by degrees (beginning at the surface) into brownish-grey, brown- 

 black, and finally into persistent yellow, the conversion being 

 effected by the oxidising influence of the air, which slowly decom- 

 poses the blue colouring matter and forms brown intermediate 

 products, all finally oxidised to a colourless compound. The 

 micro-chemical analysis of these pigment granules shows them to 

 consist of a framework of albuminous matter on which the pig- 

 ment crystals rest, but the constitution of the colouring matter 

 itself has not been established, although Beyerinck, on experi- 

 mental grounds, considers it to be allied to indigo. It resists 

 the reducing action of the bacteria in cheese, especially those 

 productive of lactic acid. 



Bacillus cyaneo-fuscus is very susceptible both to desiccation 

 on which account it is not found in atmospheric dust and 

 high temperatures, as also to acids. This explains why the 

 microbe cannot be cultivated from the blue granules in old ripe 

 cheese, since it is no longer alive therein, but has succumbed 

 under the influence of the lactic acid (of which Edam cheese, 

 for example, contains between 1.3 and 1.8 per cent.) produced 

 from lactose by the other bacteria in the cheese during the ripen- 

 ing process. Considered from this standpoint, the good result 

 obtained by so-called ropy whey (a culture of long thread and 

 lactic acid bacteria, more particularly described in Chapter xxix.) 

 as a preventive of blue grain becomes obvious. Since, as already 

 stated, oxidising agents destroy the colour, it has been proposed 

 by De Vries to decolorise blue cheese by exposing it for some 

 time to the action of oxygen in a closed vessel. 



This Bacillus cyaneo-fuscus (not infrequently met with in 

 natural waters and soils) is the sole species that as yet has been 

 positively identified as capable of producing blue grain in cheese. 

 It is uncertain whether this faculty is also inherent in other 

 organisms, though Hollman, who, in his Handboek voor den 

 Kaasmaker (" Cheesemaker's Handbook"), deals thoroughly with 

 this disease, ascribes the responsibility for its appearance to 

 Bacillus cyanogenus, an assumption which, however, according 

 to the inoculation experiments conducted in this connection by 

 Adametz and Beyerinck, is untenable. 



For the sake of completeness, it should be recorded that, 



