172 PHOSPHORESCENCE. LECT. VIII. 



in a tube, it gives out the usual ammoniacal products. It 

 does not present any obvious trace of phosphorus ; of this 

 fact I have assured myself, by calcining this matter several 

 times with nitre in a platinum crucible, and by treating the 

 dissolved residue with the tests which indicate the presence 

 of the phosphates. From all that we have now stated, we 

 can no longer regard the presence of phosphorus as the 

 cause of the light in these insects. Perhaps by operating 

 on a large number, we might succeed in discovering a slight 

 trace of phosphorus, which is usually found in all organized 

 substances. 



From all these experiments, I conclude that carbonic 

 acid is produced by the contact with oxygen of the phos- 

 phorescent matter alone, separated from the rest of the 

 animal; that the light ceases to be produced when this gas 

 is not present, and that by the contact of the latter, light 

 and a volume of carbonic acid, equal to that of the oxygen 

 consumed, are produced ; and that the phosphorescent sub- 

 stance of this insect, when not luminous, does not act on 

 oxygen. 



It is, therefore, natural to suppose, that in the luminous 

 segments of these animals, enveloped by transparent mem- 

 branes, and by means of the numerous trachea?, discovered 

 here and there in these animals, atmospheric oxygen is 

 brought in contact with a substance, sui gejieris, principally 

 composed of carbon, hydrogen, oxygen, and azote. The 

 presence of a great number of dispersed blood-globules 

 intermixed with the granular luminous matter, proves that 

 these segments are the centre of a peculiar organ of secre- 

 tion ; and I believe that this red vesicle, which I have de- 

 scribed as existing above the luminous segments, merits the 

 attention of naturalists. Excitation and heat affect the 

 phosphorescence, as they do all other phenomena of the 

 animal economy, by directly favouring combustion ; and in 



