4- 16 Dr. J. H. Pring's Observations and 



mals (the larger Medusae) exhibit, may be concluded to be 

 produced by a function in them analogous to the respiration 

 of animals which are of larger size and more complicated 

 structure. The only reason why it is visible From their bodies 

 is, that the gelatinous matter of which they consist is transpa- 

 rent. It is not improbable that the same phaenomena would 

 be as obvious in the bodies of other creatures, and even of 

 human beings, if the opacity of the materials of which we con- 

 sist did not hinder the light within us from shining so as to be 

 seen." 



From the opinion expressed by Matteucci, he would appear 

 to compare the process of vital phosphorescence to a species 

 of combustion, in which however he also recognizes the ne- 

 cessity for the presence of oxygen. In commenting on the 

 various experiments to which he subjected the phospho- 

 rescent matter, he observes, " From all these experinients, I 

 conclude that carbonic acid is produced by the contact with 

 oxygen of the phosphorescent 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 

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

 oxygen. It is therefore natural to suppose that the luminous 

 segments of theseanimals,beingenveloped by transparent mem- 

 branes, and by means of the numerous tracheae discovered 

 here and there in these animals, atmospheric oxygen is brought 

 in contact with a substance, sui generis^ principally composed 

 of carbon, hydrogen, oxygen and azote." And again, " The 

 example of an organic substance which burns in the air by 

 absorbing oxygen and emitting carbonic acid, is not new ; this 

 is the case with decaying wood, with oiled cotton, with finely 

 pulverized charcoal, and with many other substances liable to 

 spontaneous combustion." 



On this question, however, there appears to be some ground 

 for a difference of opinion. The experiment in which the Noc- 

 tilucae continued for many clays to emit very vivid scintilla- 

 tions when confined beneath an atmosphere of nitrogen, must 

 be held to militate against the preceding explanation. It is 

 asserted also by Carradori, that the Luciole will shine in a 

 barometrical vacuum, but the experiments of Matteucci on the 

 same point limit this effect to two or three minutes. Admit- 

 ting therefore the correctness of the latter observation, it may 

 still be questioned whether the effect, even for the time here 

 specified, can be wholly ascribed to the presence of oxygen. 

 Again, when operating on the phosphorescent matter only of 



