488 History of Luminescence 



phosphorus disappeared in dephlogisticated air (oxygen) ,^^ Achard 

 argued that luminous wood could not be an " insensible inflam- 

 mation." He also showed that previous illumination was not neces- 

 sary for luminescence, since a piece of wood dried in the dark would 

 again luminesce on moistening without exposure to light. Achard 

 studied the effects of many chemical substances, of which the most 

 important was spirit of wine. The luminescence did disappear in 

 this liquid but returned again (with diminished intensity) when 

 washed with water— an early, perhaps the first demonstration of the 

 reversible action of a narcotic (alcohol) on a bioluminescence. 



Achard appears to have been the first, also, to study the spectrum 

 of shining wood. When the light was observed through a prism it 

 appeared white and Achard could detect no light when the wood 

 was observed behind blue, green, or red color filters. These results 

 indicated to Achard the irrefrangibility ^^ of the light of rotten wood, 

 a finding which he regarded as " fort singulier et tres difficule a 

 expliquer " (p. 106) . 



SPALLANZANI AND CARRADORI 



After the experiments of Achard the scene shifts to Italy. The 

 next observers, Spallanzani (1796) and Carradori (1797) , did not 

 agree on the interpretation of results. The material which Spal- 

 lanzani used, called " fuochi matti " or " mad fires " by the Italians, 

 was collected from chestnut trees near Modena in August, 1795. He 

 was aware of Gottling's (1795) study of phosphorus in different 

 gases and hence placed the luminous wood, together with phos- 

 phorus, in an atmosphere of nitrogen, finding that the light of 

 both became weaker but returned to the original brightness in air. 

 Spallanzani also obtained the same result with gas from swamps 

 (probably mostly methane) . When dried, the wood frequently be- 

 came luminous if moistened. In Venice further studies with a dead 

 luminous squid *° (Sepia officinalis) showed that this type of lumi- 

 nescence also disappeared in nitrogen, returned in air, and became 

 twice as bright in oxygen. He was able to prove that the light of 

 the firefly iliicciole) likewise disappeared in nitrogen, hydrogen, 

 and CO2. From these experiments, Spallanzani drew a close analogy 

 between the behavior of phosphorus, foul fish, rotten wood, and 



^* The luminescence of phosphorus does disappear in pure oxygen (see Chapter 

 XIII) . 



" The light intensity was evidently too low to pass the particular filters which 

 Achard used. 



*" Light due to luminous bacteria. Spallanzani wished to study Pennatulae and 

 Medusae also, but they were not obtainable at Venice. 



