PHYSIOLOGY OF MICROORGANISMS 



57 



which produces a red pigment. The cell walls of some bacteria 

 (such as B. violaceus) and of many of the molds are colored. 



Pigments are generally produced only in the presence of free 

 oxygen. Cultivation at high temperatures causes some organ- 

 isms to lose the power of pigment production. Some pigments 

 are soluble in water, others in alcohol, and others in ether and 

 various fat solvents. They are of little economic importance, 

 but are of value to the systematic bacteriologist in the separation 

 and identification of species. 



LIGHT PRODUCTION BY MICROORGANISMS 

 Several species of bacteria and fungi are known that give 



Fig. 26. A bacterial lamp. The inner wall of the flask is coated with a 

 medium on which there is growing Bacterium phosphoreum. Photographed by 

 its own light (Molisch). 



off light. These are said to be photogenic. Bacteria of this 

 type are found commonly in the water of the ocean, and are 



