522 History of Luminescence 



The history of Noctiluca is of special interest, since it is one of 

 the commonest protozoa responsible for sea light, especially along 

 the Atlantic shores of Europe, and in the Far East. In fact the history 

 of sea phosphorescence is almost a history of Noctiluca. After Spar- 

 shall's letter to Baker (1753), Jean Baptiste LeRoy (1760), an 

 apothecary and professor of medicine at Montpellier, probably saw 

 Noctiluca as he examined sea water with a microscope on a trip 

 from Naples to France. He described in 1754 luminous particles 

 (" grains ") like the head of a pin, that became sparks (" etincel- 

 les ") at night and could be caught on a handkerchief. However, 

 he thought them of an oily or bituminous nature, since they did 

 not have the appearance of an animal. He noticed that the more 

 they were agitated, the less light they gave, unless they were allowed 

 to rest. Le Roy was probably the first to record this fatigue of light 

 production, a well known characteristic of Noctiluca and other 

 luminous organisms. He also found that the addition of alcohol or 

 acid and many other chemicals caused the appearance of long last- 

 ing sparks of light which finally went out, the death glow, and no 

 amount of agitation would make them luminous again. Le Roy 

 lamented that he did not have a good microscope and could not 

 leave Montpellier to work at the seashore. 



In 1757 Job Baster (1711-1775), a Dutch botanist, who tried to 

 prove that corallines were plants and not animals, recognized with 

 his microscope a number of minute " infusoria " as the cause of sea 

 light and found, as did James Bowdoin in 1753, that filtering the 

 sea water through blotting paper would remove the organisms and 

 the luminescence. 



In 1762 Pehr Forskal (1736-1763) , professor of natural history 

 in Copenhagen, confirmed the filtering experiment and described a 

 number of new marine luminous forms. He noted that the peri- 

 phery of Noctiluca, called by him " medusa noctiluca," luminesced 

 more markedly than the center. 



In 1765 M. Rigaut, a " Physicien de la Marine " at Calais, de- 

 scribed Noctiluca so minutely that it could be easily recognized. 

 He had been asked by the Abbe Nollet to see whether the phospho- 

 rescence of the sea at Calais was due to animacules. In carrying out 

 the experiment, he added small amounts of various acids (HCl, 

 HNO3, H2SO4 and acetic) to the sea water and discovered, like 

 Baster, that the small " insects " therein luminesced continuously 

 and then the light disappeared. There was no return of lumines- 

 cence on neutralization. At present most observers use ammonia 

 rather than acid for this purpose because ammonia will excite a 

 more lasting light, thereby allowing more time to identify the lumi- 



