124 NATURAL HISTORY. [CH. VII. 



creased by heat and oxygen, and extinguished by 

 cold, also by hydrogen and carbonic acid gas. Mr. 

 Murray has ascertained, by experiments, " that the 

 light is not sensibly increased by the purest oxygen, 

 and is not extinguished in hydrogen and carbonic 

 acid gas ;" and he found that the luminous matter 

 continued to shine, without alteration, in oxygen, 

 nitrous oxyde, hydrogen, carbonic acid gas, cyano- 

 gen, olefiant gas, and nitrous gas ; and the light is 

 not extinguishable by being placed in water, oil, or 

 even in different kinds of acids, such as muriatic, 

 nitric, and sulphuric, but continued for some seconds. 

 In a solution of pure caustic potassa it became of a 

 bluish teint, and appeared to undulate ; and in tinc- 

 ture of iodine the light continued for a minute. In 

 alcohol it lasted nearly two, and in ammonia it con- 

 tinued for a minute. 



It has lately been discovered by Dr. Carus, of 

 Dresden, that there is a connexion between the cir- 

 culation of the blood in the Lampyris Italica, or 

 Italian glow-worm, and the luminous matter which 

 occupies a great part of the under side of the abdo- 

 men, and that the varying intensity of the light is 

 thus produced ; the greater intensity corresponding 

 precisely with each pulsation of that fluid: being 

 from forty-four to fifty-four times in a minute, when 

 the insect is not disturbed, but more rapid and irreg- 

 ular when alarmed. 



Some authors are of opinion that there exists a 

 sensible degree of heat in the luminous matter, for 

 it has been stated that the thermometer was affect- 

 ed by nearly a degree when the insect was allowed 

 to pass over its bulb ; while others have asserted 

 that no heat is perceptible. 



Mr. Murray is of opinion that the luminous sub- 

 stance remains permanently luminous, and the eclipse 

 seems entirely occasioned by the spherulae, in which 

 the luminous principle resides, being withdrawn by 

 a contractile movement into the darker recesses of 



