102 BIOLOGICAL LECTURES. 



But viewed from the standpoint of cell physiology, the phe- 

 nomena of animal phosphorescence is the result of physico- 

 chemical changes in the living protoplasm, probably of the 

 same nature as that of heat production, the only peculiarity of 

 the former being that it manifests itself in such a form as to 

 affect the most potent of our special senses, the sense of 

 sight, and the latter, the sense of temperature. 



On a priori ground it is easily conceivable that the animal 

 that produces heat, as all animals can, may just as well produce 

 light under certain circumstances, for both are but the mani- 

 festations of the same energy, and can be produced by essen- 

 tially the same physico-chemical antecedents. 



The production of light by the living organism becomes still 

 more interesting, and appears unique when we remember that 

 the light thus produced is not accompanied by any sensible 

 heat. 



" You gaudy glow-worms, carrying seeming fire, 

 Yet have no heat within ye ! " 1 



This difference between the light produced by the activity 

 of the living organism and by the purely artificial process has 

 also been pointed out by the natural philosopher, Robert Boyle. 

 In one 2 of his several contributions on the subject he says: 

 " That whereas a coal, as it burns, sends forth store of smoke 

 or exhalations, luminous wood does not so " ; and " that whereas 

 a coal in shining wastes itself at a great rate, shining wood does 

 not"; and "that a quick coal is actually and vehemently hot, 

 whereas I have not observed shining wood to be so much as 

 sensibly lukewarm." 3 



The same peculiarity in the light of the living substance has 

 been recognized by Faraday, Matteucci, Young, Langley, and 

 Very, and by the last two it has been made the subject of a 

 beautiful research within recent years. 



1 Fletcher: The Elder Brother, act iv, sc. i, 1637. 



2 R. Boyle : Observations and Trials about the Resemblances and Differences 

 between a Burning Coal and Shining Wood, Phil. Trans., No. XXXII, 605, 1667- 

 1668. 



8 It is hardly necessary to say that Boyle was not aware of the fact that the 

 luminosity of the shining wood is caused by the activity of the living organism. 



