382 



In none of these animals could Mr. Macartney discern that the 

 luminous organs were supplied either with nerves, or with air tubes, 

 better than other parts of their bodies. 



With the exception of these insects, in which the light is confined 

 to particular parts, the exhibition of light appears to the author to 

 depend on the presence of a fluid matter diffused throughout the 

 whole body of the animal. 



By squeezing the fluid of two large Medusas into a glass of well- 

 water, it was rendered luminous for nearly an hour and a half. Agi- 

 tation also occasioned a fresh appearance of light after that period, 

 and even after agitation ceased to produce any effect, an increase of 

 temperature rendered it again luminous for a short time. 



Since the phenomena of animal light have been attempted to be 

 explained in various ways by different authors, and since their expe- 

 riments are in many respects at variance with each other, the author 

 adds a series of experiments of his own, from which he draws his 

 own conclusions. 



A glow-worm lived, and emitted light, nearly two hours in a glass 

 of water, though thus confined from oxygen. 



The luminous substance, after being extracted from glow-worms, 

 gave no light. 



The luminous sacs, on the contrary, after having been cut out from 

 the tail of the glow-worm, continued to emit light several hours in 

 the atmosphere ; and when put into water the power was prolonged 

 to forty-eight hours. 



By application of heat they were not rendered more luminous, and 

 had no tendency to active combustion, like phosphorus. 



The luminous part of the glow-worm appeared to raise a delicate 

 thermometer, somewhat more than other parts of its body ; but of 

 this fact the author is not confident : but when the luminous sacs 

 had been separated from the body of the animal, these had no effect 

 on the thermometer, though they continued to emit light. 



By heating some water containing Medusae, the brilliancy of their 

 light was very much increased ; but they were killed in less than a 

 minute. 



Some of the same Medusae, being put into spirits of wine, emitted 

 immediately a strong light, which continued till they died. 



The Medusa scintillans, or hemispheerica, being put under the re- 

 ceiver of an air-pump, in a vessel of water, continued to emit light, 

 notwithstanding complete exhaustion of the air. 



A Medusa, upon being electrified by sparks from an electric ma- 

 chine, was not excited to give out light. But when shocks were 

 transmitted through a collection of Medusae hemisphcerictE, they were 

 excited, and shone with great brilliancy. 



From these experiments, says the author, it appears that the lu- 

 minous substance is by no means of the nature of phosphorus, as it 

 often shows the strongest light when excluded from oxygen gas ; and 

 so far from undergoing any process of combustion, it is incapable of 

 being inflamed ; that the increase of heat during the shining of glow- 



