JUNE 101 



'My hand is not so steady,' he says, 'nor my sight so 

 good as once they were ; but, so far as they allow me, I con- 

 sult anatomy for the structure of the luminous organs. I 

 take a scrap of the epidermis [of a female glow-worm] and 

 manage to separate pretty nearly half of the shining belts. 

 I place my preparation under the microscope. On the skin 

 a sort of whitewash lies spread, formed of very fine granular 

 substance. This is certainly the light^producing matter. 

 To examine this white layer more closely is beyond the 

 power of my weary eyes. Just beside it is a curious air-tube, 

 whereof the short and remarkably wide stem branches 

 suddenly into a bushy tuft of very delicate ramifications. 

 These creep over the luminous sheet, or even dip into it. ... 

 The luminescence, therefore, is controlled by the respiratory 

 organs, and the result is that the white material is oxidised 

 by the action of the tube and its branches distributing a flow 

 of air over it. There remains the question of the substance 

 whereof the white sheet is formed. The first suggestion 

 was phosphorus, in the chemist's sense of the term. The 

 glow-worm has been calcined and its ashes treated with 

 violent re-agents that bring the simple substances to light ; 

 but no one, so far as I know, has obtained a satisfactory 

 answer along these lines. Phosphorus seems to play no part 

 here . . . the answer lies elsewhere. ' 



Fabre was not content with guessing that the light 

 was the result of oxidisation. He proved that portions 

 of the white sheet retained their luminosity after being 

 removed from the insect, so long as they were exposed 

 to the air. Plunged into boiled, and therefore de-oxy- 

 genated, water the light was instantly extinguished ; 

 but when placed in serated water containing plenty of 

 free oxygen, the light reappeared. Fabre found by 

 repeated experiment that the female glow-worm can 

 heighten the illumination by directing a puff of air on 



