THEORY. 193 



evidence of combustion being the cause of the 

 light of glowworms may be thus stated : 



1. Matteucci and Koberts, the former by very 

 delicate experiments, assure themselves that a 

 slow combustion takes place, though no sensible 

 heat is evolved. They do not know what sub- 

 stance burns; they find, however, that the light, 

 though not immediately extinguished in hydrogen 

 and carbonic acid, is so in about half an hour ; 

 whilst, in oxygen gas, it shines three times longer : 

 that is, at least an hour and a half. 2. M. Schnetz- 

 ler finds phosphorus in the luminous tissue of the 

 insect, after oxidizing it with nitric acid, in the 

 state of phosphoric acid or phosphates ; and this 

 phosphorus may have been present as free phos- 

 phorus, since Mr. Thornton Herapath finds no 

 phosphates in the insect's body. 3. Professor 

 Morren, as Macartney had done before him, 

 shows that large air-tubes or tracheae are inti- 

 mately connected with the luminous tissue; and 

 Morren shows further that the animal extinguishes 

 its light by closing the spiracula or air-orifice 

 through which the air enters the luminous organ. 

 4. The luminous substance shines for some time 

 after death, as if phosphorus were really present, 

 especially when damp. 



Until these facts, which tend to prove that the 

 phosphorescence of glowworms is a phenomenon 

 of combustion, be confirmed or refuted by fur- 



o 



