152 CHROMOPAROUS BACTERIA. 



it may prejudicially affect the health of the animals and the com- 

 position of the milk, as was ascertained by E. HESS, F. SCHAFFER, 

 and M. LANG (I.). The milkers' hands and the cows' udders 

 should be carefully washed before milking. The sudden appear- 

 ance of the evil, and its frequent disappearance after a change of 

 fodder, permit the conclusion that the bacillus occurs not infre- 

 quently on certain vegetables, from which it finds its way into the 

 dung of the animal and thence into the milk. 



As has already been stated, the blue coloration of milk by 

 bacterial agency is effected gradually when the liquid is left to 

 stand, and first makes its appearance on the surface. If, on the 

 other hand, the milk is of a bluish or blue colour when freshly 

 drawn, this results from the cow having partaken freely of the 

 flowering rush (Butomus umbellatus), which contains a blue colour- 

 ing matter (indigotin 1) that is taken up by the gastric juices, 

 conveyed in an unaltered condition into the arterial circulation, 

 and thus finds its way into the milk. 



95. Blue Coloration in Cheese. 



This is an evil to which the Dutch dairy industry is particu- 

 larly liable. Since it very often makes its appearance only after 

 the ripening stage is over that is to say, at a time when the 

 article has already passed into the hands of the salesman it is the 

 cause not only of monetary loss to the cheese-maker, but also of 

 unwelcome complaints on the part of the purchaser. The pheno- 

 menon manifests itself in various forms. Either the whole bulk 

 of the cheese is of a bluish cast, or exhibits blue patches inter- 

 nally, or, finally, is interspersed with blue spots (Dutch, "stipjes") 

 from i to 2 m.m. (-^ to jV inch.) in diameter, the latter form 

 (blue grain : Dutch, " blauwstippigkeit ") being the most common. 



The causes of blue cheese are twofold ; one of them being 

 chemical, and due to iron sulphide, as was demonstrated by 

 M. SCHMOEGER (I.) and TH. KLARVERWEIDEN (I.). Normal cheese 

 contains but a very small quantity of iron ; Cheddar, for instance, 

 having 0.009 P er cent. ; Gouda, o.on per cent., and so on. If, 

 however, a larger quantity of iron obtains admittance to the milk 

 or freshly precipitated curd, it will then gradually, during the 

 ripening process, enter into combination with the sulphuretted 

 hydrogen separated from the albumin by bacterial action, and 

 will form iron sulphide, which, as is well known, exhibits a blue 

 shade when in a dilute condition. When the iron has been 

 admitted in the soluble form, then cheeses coloured a fairly uni- 

 form blue or bluish shade throughout will result. If, on the 

 other hand, the metal be present in coarser particles, e.g. in the 

 form of rust, then a patchy-blue or blue-grained cheese will be 

 obtained. This explains the more frequent occurrence of the 

 phenomenon since the introduction of the centrifugal machine 



