LIGHT-PRODUCING ORGANISMS 17 



in which the skin was the source of light, especially if 

 the person sweated freely. It is possible that here we 

 are again dealing with luminous bacteria upon the accu- 

 mulations of substances passed out in the sweat, which 

 serves as a nutrient medium. 



There are also on record, in the older literature, cases 

 of luminous urine, where the urine when freshly voided 

 was luminous. If these observations are correct and they 

 may, perhaps, be doubted, we are at present uncertain of 

 the cause of the light. Bacterial infections of the bladder 

 are not inconceivable although luminous bacteria are 

 strongly aerobic and would not thrive under anaerobic 

 conditions. I can state from my own experiments that 

 luminous bacteria will live in normal human urine, but 

 not well. In albuminous urines it is very likely that they 

 would live better, and it is possible that the luminous 

 urines reported are the results of luminous bacterial 

 infection. On the other hand, the light may be purely 

 chemical, due to the oxidation of some compound, an 

 abnormal incompletely oxidized product of metabolism, 

 which oxidizes spontaneously in the air. We know that 

 sometimes these errors in metabolism occur, as in alkapto- 

 nuria, where homogentistic acid is excreted in the urine 

 and on contact with the air quickly oxidizes to a dark 

 brown substance. Light, however, has never been re- 

 ported to accompany the oxidation of homogentistic acid, 

 although it does accompany the oxidation of some other 

 organic compounds. (See Chapter II.) 



Finally, we may inquire to what extent luminous 

 animals may be utilized by man. Leaving out of account 

 the use of tropical fireflies for adornment by the natives 

 of the West Indies and South America and the use for bait, 



