98 PHYSIOLOGICAL ACTIVITIES 



hence they are frequently found on various sea foods, espe- 

 cially when these are allowed to decompose, such as fish, 

 oysters, clams, etc. The light is due to the conversion of 

 the energy of unknown easily oxidizable compounds directly 

 into visible radiant energy through oxidation without appre- 

 ciable quantities of heat. The light produced may be 

 sufficient to tell the time on a watch in absolute darkness, 

 and also to photograph the growths with their own light, 

 but only after several hours exposure (Fig. 66). None of 

 the phosphorescent bacteria so far discovered produce 

 disease in the higher animals or man. 



PRODUCTION OF PIGMENT OR CHROMO GENE SIS. 



One of the most striking results of bacterial activity is 

 this phenomenon. The particular color which results may 

 be almost any one throughout the range of the spectrum, 

 though shades of yellow and of red are of more frequent 

 occurrence. 



In the red sulphur bacteria the " bacterio-purpurin" which 

 they contain appears to serve as a true respiratory pigment 

 in a manner similar to the chlorophyl in green plants, except 

 that these bacteria oxidize H2S in the light as a source of 

 energy instead of splitting up CO2. The red pigment pro- 

 duced by certain bacteria has been shown to have a capacity 

 for combining with O resembling that of hemoglobin, and 

 some investigators have believed that such bacteria do 

 store O in this way for use when the supply is diminished. 

 With these few exceptions the pigments seem to be merely 

 by-products of cell activity which are colored and have no 

 known function. 



The red sulphur bacteria above mentioned and one or 

 two other kinds retain the pigments formed within the cell. 

 Such bacteria are called chromophoric as distinguished from 

 the chromoparic bacteria whose pigment lies outside the cell. 



The chemical composition of no bacterial pigment has 

 been determined up to the present. Some are soluble in 

 water, as shown by the discoloration of the substances on 

 which they grow. Others are not soluble in water but are 



