Mr. Macartney's Observations 
282 
Spallanzani discovered a mucous luminous fluid in the 
plumule of the pennatula phosphorea.* 
The phenomenon of animal light has been attempted to be 
explained in different ways. By many persons it was formerly 
ascribed to a putrefactive process, but since the modern 
theories of combustion became known, it has been generally 
believed to depend upon an actual inflammation of the lumi- 
nous substance, similar to the slow combustion of phosphorus. 
Others have accounted for the luminous effect, by supposing 
the matter of light to be accumulated, and rendered latent 
under particular circumstances, and afterwards evolved in a 
sensible form. 
The opinion of the light of living animals being the con- 
sequence of putrefaction, is evidently absurd, and contradictory 
to all observation on the subject. It has been proved by the 
experiments of Dr. Hulme and others, that even the luminous 
appearances of dead animals, are exhibited only during the 
first stages of the dissolution of the body, and that no light is 
emitted after putrefaction has really commenced. 
Spallanzani, who was the most strenuous advocate for the 
phosphorescent nature of animal light, stated that glow- worms 
shone more brilliantly when put into oxygen gas ; that their 
light gradually disappeared in hydrogen or in azotic gas, 
and was instantly extinguished in fixed air ; that it was also 
lost by cold, and revived by the application of a warm tem- 
perature. He conjectured that the luminous matter of these 
insects was composed of hydrogen and carbonated hydro- 
gen gas. 
Forster relates, in the Lichtenberg Magazine for 1783, 
* Mem. della Soc. Ital. Tomo ii. 
