THEORY. 193 
evidence of combustion being the cause of the 
heht of glowworms may be thus stated :— 
1. Matteucci and Roberts, 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 lght, 
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 hourand a half. 2. M. Schnetz- 
ler finds phosphorus in the luminous tissue of the 
insect, after oxidizing vt with nitric acid, in the 
state of phosphoric acid or phosphates ; and this 
phosphorus may have been present as free plhos- 
phorus, since Mr. Thornton Herapath finds no 
phosphates in the insect’s body. 38. Professor 
Morren, as Macartney had done before him, 
shows that large air-tubes or trachez 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- 
fe) 
