122 CHROM OP ARGUS BACTERIA 



98. Green Bacteria 



were observed by Schroeter, and COHN (I.) named one such species (producing a 

 sap-green colour) Micrococcus chlorinus. VAN TIEGHEM (III.) introduced into the 

 literature of the subject two new green non-motile species under the names of 

 Bacterium viride and Bacillus virens. The Bacterium chlorinum, discovered by 

 ENGELMANN (VII.), is more highly interesting. It is endowed with powers of 

 locomotion, and when present in microscopic preparations where there is a lack 

 of oxygen it strives to reach such spots as are illuminated by white, yellow, 

 or red light. The three last-named species are not chromoparous, but chromo- 

 phorous bacteria. W. SYMMERS (I.) described a Bacillus viridans. Reference may 

 be made in this place to a treatise on the green bacteria by P. A. DAXGEARD (I.). 

 Green fluorescent transformation products are excreted by very many species 

 of bacteria, a number of which are described in Eisenberg's work. At present 

 mention of three will suffice, viz., the gelatin-liquefying Bacillus fluorescens ligue- 

 faciens, and the Bacillus fluorescens non-liquefaciens, which grows on the same 

 medium into solid colonies. Both organisms occur in natural waters. The 

 author in 1891 discovered a fission fungus of very frequent occurrence in Munich 

 butter, and named it Bacillus butyri fluorescens. 



C. GESSARD (V.) recorded a beautiful observation in connection with the 

 formation of fluorescent pigment by Bacillus pyocyaneus. This substance is in 

 the case of nutrient solutions prepared artificially from mineral salts produced 

 only when phosphates are present in quantity equivalent to at least 0.25 grm. of 

 potassium phosphate per litre. When this supply is reduced, the organism 

 develops, but produces no fluorescence. This behaviour is also exhibited by 

 other fluorescent bacteria, so that these can therefore be regarded as very delicate 

 tests for potassium phosphate. 



K. THUMM (I.) comparatively examined a number of bacterial species 

 yielding fluorescent cultures, viz., Bacillus fluorescens tennis, B. fl. putidus, B.fl. 

 albus, B. erythrosporus, B. viridans, B. pyocyaneus, Bacterium syncyaneum 

 (Bacillus syncyaneus). These species produce, in alkaline gelatin, a fluorescence 

 initially sky-blue, but afterwards moss green, caused by an excreted yellow 

 pigment, which is formed only when the medium contains magnesium sulphate 

 and potassium phosphate. 



The green coloration of cheese is, as first determined by CARLO BESANA (I.), 

 due to the presence of copper, this evil being especially manifested by Lodisan 

 cheese, the Parmesan cheese produced in Lombardy formagyio di grana 

 lombardo. The initially yellow cut surface of this cheese becomes green by 

 exposure to the air. For the successful preparation of this cheese a certain 

 fairly high degree of acidity in the milk equal, according to J. RAY! (I.), to 

 0.22 per cent of lactic acid is essential, and therefore it is the custom in 

 Lombardy to leave the milk to acidify -in untinned copper vessels, whereby it 

 takes up a considerable quantity of copper. In fact, the progress of the souring 

 is determined by the gradual disappearance of the metallic lustre from the 

 previously polished surface of the vessels. G. MARIANI (I.), who examined 

 twenty-five samples of these cheeses for their content of copper, found the 

 minimum to be 54 mgrms. of Cu per kilogrm. of cheese, and the maximum 215 

 mgrms., the average per kilo, of Lodisan cheese being 100-110 mgrms. of 

 copper. That this metal alone is actually responsible for the green coloration of 

 cheese is evidenced not only by comparative laboratory experiments with tinned 

 and untinned milk vessels, but also by the fact that the Parmesan cheeses made 

 south of the river Po (especially in Reggio), and brought to Parma for sale, 

 undergo no alteration in their yellow colour when cut. In that region, however, 

 the milk is left to acidify in wooden tubs. 



