PHYSIOLOGICAL LIGHT. 427 



conflagrations and never being extinguished by the winds nor the rain, 

 being, in fact, an ideal illuminant. Neither need it be supposed that 

 these little lanterns which they always carry with them, and which they 

 can use at any moment, cause any great expenditure, for the total loss 

 of weight of twenty Pyrophori in three days and three nights during 

 which they had shone for long hours was found by experiment to be 

 0.063 gram — that is to say, about 0.03 gram per insect, and during 

 that time they had expended much more energy in movement than in 

 light and had consumed no nutriment. Was I not right when 1 said 

 in the first place that this physiological light ought, by its composi- 

 tion, to serve as a type for the artificial light of the future, and have 

 not the recent applications of zirconium to illumination already partly 

 shown the accuracy of my predictions'? Up to 1886, when I published 

 my first researches, nothing was thought of but the perfecting of the 

 illuminating apparatus then in use. I believe that I opened a new and 

 promising field for future progress by showing the inferiority of these 

 means when compared with those of nature and by placing the ques- 

 tion upon the ground of producing illumination by a new method. 



II. 



Everything goes to prove that there is no analogy between the actual 

 mechanism of the photogenic function and our industrial methods, and 

 we are far from the artless explanation of the blast tubes for burning 

 up the protoplasm, but the analysis of the physiological mechanism of 

 the photogenic organs, and even that of the intracellular modifications 

 that accompany luminous emission (discussed in the first part of this 

 article), have not answered the philosophical question, much more 

 important for us than the economic one: Is the production of physio- 

 logical light reducible to a simple physical or chemical phenomenon ? 



We know now that the ultimate element of the phenomenon is 

 physical. Let us examine the work of the vital function. 



It will be remembered that the photogenic organ of Lampyra dried 

 and pulverized still gives out light when the amorphous dust is mois- 

 tened with a drop of water. This simple experiment, which may be 

 repeated with a multitude of other photogenic organisms, suffices to 

 prove that it is neither in the structure nor in the working of the 

 organ or of the photogenic cell that we must seek for the ultimate 

 cause of the emission of light. 



For simplicity, we will first confine ourselves to the consideration 

 of the photogenic matter furnished by Plwlas dactylus, because that 

 mollusk produces it freely and quite abundantly in the form of a 

 liquid that remains luminous even after being filtered, then containing 

 in suspension only fine protoplasmic granulations that give it a cloudy 

 appearance. These semifluid granulations, which I have called 

 vacuolides because of the appearance that they present under the 



