u8 CHROMOPAROUS BACTERIA 



tinning of the interior of the cylinder is therefore advisable, and should be 

 renewed in good time. One observation made by Klarverweiden still remains to 

 be mentioned, viz., that the frequency of the occurrence of blue cheeses in Holland 

 is coincident in point of time (August and September) with the highest per- 

 centages of the iron bacterium, Crenothnx Kilhniana, in natural waters. 



Blue cheese may, however, also result from the activity of micro-organisms. 

 H. DE VRIES (I.), in 1887, asserted that a microscopical examination showed 

 that the blue dots in question ought to be considered as colonies of a blue pig- 

 ment bacterium ; but he made no attempt to prepare cultures thereof. The 

 subject of his investigations was Edam cheese, a kind very frequently affected 

 by blue grain. BEYERINCK (X.) identified, as the cause of this disease, a fission 

 fungus which he named Bacillus cyaneo-fuscus. However, before proceeding to 

 the consideration of the properties and functions of this organism, we must 

 devote a little attention to the microscopy of cheese. 



The structure of sound cheese, as exemplified by the appearance of thin 

 sections immersed in water under the microscope, is made up of the following 

 elements. The ground mass or matrix consists of amorphous casein enclosing 

 small drops of fat and bubbles of gas, which are, however, for the most part, not 

 spherical, but irregular in outline, owing to the pressure of the enveloping curd. 

 Along with these two enclosures readily detectable by their optical and micro- 

 chemical behaviour a closer examination will reveal crystalline spheroids of a 

 substance allied to or identical with tyrosine ; also yeast cells, and, finally, a 

 large number of bacteria. The crystalline spheroids are oval or kidney-shaped, 

 and about as large as big yeast cells (some 10 p long by 8 /* broad). Each of 

 these crystalline aggregations exhibits (like starch granules) a central nuclear 

 spot, around which the crystal needles are arranged radially, and constitute in 

 their- totality a crystalline spheroid. A thin section cut from a blue patch or 

 speck of a blue cheese reveals, in addition to these normal constituents, sundry 

 granules of colouring matter, mostly bluish-black, but frequently brownish in 

 colour, and forming the actual pigmentary substance. The crystalline spheroids 

 are also highly coloured. Bacteria will be found more plentifully assembled in the 

 centre of the blue patch or dot than in any other position. The (usually globular) 

 colour granules, the diameter of which varies from i to 5 /u, are an excretory pro- 

 duct of the acillits c^aneo-fuscus, which can be isolated from the blue patches. 



The dimensions of this motile microbe vary according to the conditions of 

 nutrition. On nutrient gelatin the cells grow to a length of 1.0-1.5 /* D 7 

 0.2-0.3 fj, in breadth ; whereas in a solution of 0.5 per cent, of peptone in ditch- 

 water they only develop to 0.3-0.6 /z by 0.15 /*. 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 

 decomposes 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 pigment crystals rest, but the constitution of the colouring 

 matter itself has not been established, although Beyerinck, on experimental 

 grounds, consideis it to be allied to indigo. It resists the reducing action of the 

 bacteria in cheese, especially those productive of lactic acid. 



