PHYSIOLOGICAL LIGHT. 425 



the wave-length ).i 0.485,68, and is consequently thrown back on the 

 side of the more refrangible rays. An inverse result would have been 

 obtained if the peculiar appearance of the spectrum of Pyrophorus was 

 due only to its relatively feeble intensity, since in that case the blue 

 rays would seem more abundant. Finally, in the ease of the candle, 

 the yellow rays fall in a narrower part of the area between the curve of 

 intensity and the line of wave-lengths. 



In comparing these areas with each other, we find that the spectro- 

 photometry value of one of the two protlioracic lanterns of a Pyrophorus 

 would be about one one hundred and fiftieth of a Phosnix candle (8 to 

 the pound). If we admit that the ventral apparatus possesses an 

 illuminating power double that of the prothoracic ones, we see that it 

 would take from thirty-seven to thirty-eight Pyrophori, all luminous 

 at once with their three apparatuses, to illuminate an apartment with 

 the same intensity as a candle. 



The average wave-length of this light, obtained either by calculation 

 or graphically, is found to be between /< 0.530 and /< 0.533, nearly 

 that of the green line of thallium /< 0.535; and, indeed, the light of 

 Pyrophorus is very similar to that of the sun shining through foliage 

 (9a\\6$, a green branch). 



It should be added that this spectrum is not at all like that of phos- 

 phorus burning in oxygen or hydrogen, and hence we can at once reject 

 certain hypotheses relative to the special mechanism of the photogenic 

 function. The green color of the light of Pyrophorus is increased by 

 the existence of green matter in the blood, which bathes abundantly 

 the photogenic organs during their action. But besides its special 

 coloration, it possesses a peculiar opalescent luster, on account of which 

 all observers speak of it as of beautiful clarity. 



This clarity recalls that of fluorescent substances, and it is this that 

 led us to discover in the blood of Pyrophorus a material that becomes 

 luminous when exposed to the influence of the ultra violet rays, espe- 

 cially those having a wave-length of pi 0.391. Dilute acetic acid 

 annuls this fluorescent power, while ammonia restores it. Now, both 

 these reactions affect similarly the photogenic power of all substances, 

 animal or vegetable, and this has led us to think that the production 

 of physiological light was due to the transformation of obscure vibra- 

 tions, depending on protoplasmic molecular movement, into luminous 

 undulations. But this substance not having been found in the lumi- 

 nous creatures, there is reason to believe that its function is limited to 

 transforming into luminous rays and throwing toward the middle por- 

 tion of the spectrum the chemical rays that originate simultaneously 

 with the luminous rays in Pyrophorus. Thus reenforced, the middle 

 portion of the spectrum forms what might be called a focus of condensed 

 light. I have given to the transforming substance whose composition 

 is unknown, but whose existence can not be doubted, the name of 

 pyropliorine. 



