BLUE COLORATION IN CHEESE. 155 



into the dairy industry, the numerous rivets of the iron cylinder 

 of this machine being, as demonstrated by Schmoeger, so many 

 sources of contamination of the milk by rust. Careful 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 percentages of 

 the iron bacterium, Crenothrix Kulmiana, in natural waters. 



Blue cheese may, however, also result from the activity of 

 micro-organisms. H. DE VRIES (I.), in 1887, asserted that a micro- 

 scopical examination showed that the blue dots in question ought 

 to be considered as colonies of a blue pigment 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 appear- 

 ance 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 iden- 

 tical with tyrosine j 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 /x 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 colour- 

 ing 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 ju,, are an excretory product 

 of the Bacillus cyaneo-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 A* by 0-2-0.3 ft in breadth ; whereas in a solu- 



