BACTERIAL PIGMENTS 133 



most at will, and even to develop races of bacteria that do not produce 

 pigment at all, from races that ordinarily are pigment-producers. 



Of nuniorous classifications of pigment-forming bacteria, all faulty 

 because of our slight knowledge of the chemistry of the process, that 

 of Migula seems the best; it is based on the solubility of the pigments 

 formed, as follows: 



(1) Pig-ments Soluble in Water. — This includes the pigments of 

 all fluorescent bacteria, as well as those giving a red or brown color 

 to gelatin media. Most important among these is Bacillus pyo- 

 cyaneus, whose pigments have been considerably studied. There seem 

 to be two pigments, one, pyocyanin, characteristic for this organism; 

 and a fluorescent pigment which numerous other organisms also pro- 

 duce. Pyocyanin has been analyzed by Ledderhose, who found it to be 

 a ptoma'in-like body, a derivative of the aromatic series, probably re- 

 lated to the anthracenes. It can be reduced to a colorless leuco-base, in 

 which form it is probably produced by the bacteria, and then is 

 oxidized in the air into the pigment. Its composition is Cj^Hj^NoO 

 (the sulphur-containing pyocyanin which has been described is proba- 

 bly impure). The fluorescent pigment is insoluble in alcohol and 

 chloroform, and can thus be separated from pyocyanin, which is solu- 

 ble in chloroform. Although related to the ptomains, pyocyanin seems 

 to be altogether non-poisonous to animals. 



Jordan ^* and Sullivan ^^ have studied the conditions under which 

 pigments are formed, and found that pyocyanin can be produced in 

 protein-free media, and without the presence of either phosphates or 

 sulphates; but both sulphur and phosphorus must be present to pro- 

 duce the fluorescent pigment. As pigments can be produced on media 

 containing only ammonium salts of succinic, lactic, or aspartic acid, 

 or asparagin, they are evidently formed synthetically, and not by 

 cleavage of the media. 



(2) Pigments Soluble in Alcohol and Insoluble in Water. — The most 

 important bacteria of this group are the Staphylococcus pyogenes 

 aureus and citreus. Their pigment is of a fatty nature, a lipochrome, 

 which lies among the bacteria in the form of dendritic crystals. Be- 

 ing a fat, it can be saponified, and when decomposed it gives the 

 acrolein reactions and odor, from the breaking down of the glycerol 

 of the fat molecule. Acted upon by strong sulphuric acid, the yel- 

 low pigment changes into blue granules and crystals {lipocyanin re- 

 action). The lipochromes are soluble in the usual fat solvents, and 

 fonn fat spots on paper. 



(3) Pigments Insoluble in Water and in Alcohol. — The pigment of 

 Micrococcus cereus flavus belongs to this class; its nature is quite un- 

 known. 



i*Jour. Exper. Med., 1899 (4), 627. 



