THE CHEMISTRY OF BACTERIA 51 



we have organisms which produce all the colors of the rainbow. 



The phenomenon of pigment production has long attracted 

 the attention of the scientist and many attempts have been made 

 to explain its function, but so far none of the explanations would 

 seem to be wholly satisfactory. The color seems to be of no ma- 

 terial advantage to the bacteria, for colorless strains may be culti- 

 vated which possess all of the properties of the original strain with 

 the exception of pigment production. There is no evidence that 

 they protect the organism against light, nor is there anything 

 that would lead us to believe that they are similar to the hemo- 

 globin of the blood or the chlorophyll of the green plants. The 

 best evidence, therefore, points to the conclusion _ that they are 

 mere by-products which have no particular meaning to the or- 

 ganism. 



Light. — Most individuals have been mystified and delighted, 

 if not frightened, by the uncanny beautiful light which at times 

 covers a stump in the forest. At times, especially along the sea- 

 shore, it seems to be emitted as a mysterious yet beautiful phosphor- 

 escence from the sand. One writer tells of a cluster of sausages 

 brought to his laboratory. It was hung in a dark cellar and 

 when the maid went for it in the morning there "hung in the 

 place of the sausage a fiery .fBgy which seemed to her more like 

 the quondam spirits of their mysterious ingredients than the unc- 

 tuous homely friend of the homeless boarder." 



The explanation of these apparent mysteries is that certain 

 bacteria live on decaying wood, leaves, salt water, meat, and fish, 

 and emit a light. Pure cultures of these peculiar bacteria have 

 been grown in test tubes placed alongside a watch and photo- 

 graphed by their own light, the light being bright enough for 

 one to see the hour and minute hands of the watch. The mys- 

 tery today is-what is the fuel that burns in these tiny lanterns 

 and how can they so economically produce from it light? 



Heat. — Probably all bacteria liberate heat, and there are a 

 number which liberate it in sufficient quantity to change the tem- 

 perature of the medium in which they grow. This is observed in 

 the heating of fermenting silage, manure, and hay. At times the 



