BASIS OF ANIMAL PHOSPHORESCENCE. 103 



Readers of the Life of Faraday will notice what a lively 

 interest he took in the luminous phenomena of the fire-fly and 

 the glow-worm. The journaP he kept during his travel over 

 the continent with Sir Humphry Davy in 18 14, when Faraday 

 was twenty-two years old, makes frequent mention of his experi- 

 ments with the luminous phenomena of the fire-fly and the glow- 

 worm. I quote him at length because he correctly surmised all 

 the results of his later workers, and also because his unassuming 

 but remarkable record of his observations has escaped the notice 

 of writers on animal phosphorescence subsequent to the publi- 

 cation of Faraday's Life. (Italics are mine.) 



" On the way home many fire-flies appeared, emitting their 

 transient light. ^ I caught several ; and on arriving at the 

 house endeavored to ascertahi wJietJier the luminous appearance 

 depended on the life of the fly. I found one apparently dead ; 

 and separating the part which emitted light from the rest of 

 the body, it appeared filled with a white glutinous matter, 

 which, when extended and exposed to the air, shone for about 

 a minute. 



" I killed a fly suddenly, and separated the matter. It was 

 shining at the moment I killed it ; but when dead it ceased to 

 shine. On separating the part and exposing it to the air it 

 immediately shone brightly as when attached to the fly, and 

 over the whole surface, although only the section was exposed 

 to the air. It at length became dim ; but on compressing 

 it, and exposing a fresh part to the air, it shone brightly 

 as at first, and thus it continued luminous for above forty 

 minutes. At last it became totally extinct ; and the same 

 effect took place with other flies treated in the same manner. 

 It is probable, from the intermitting and regtilar appear- 

 ance of the light, that it has a dependence on the respiration ; 

 and at least it is evident that air is sufficient to cause this 

 matter {probably a secretion) to shine. No heat was sensible 

 to the hands or to the underlip {the most delicate part of the 

 body) . ' ' 



1 Dr. Bence Jones : Life and Letters of Faraday, Vol. I, 1S70, pp. 90, 91, 125, 

 141, 142, 144-146. 



2 Friday, June 3, 1S14 (Terni), Italy, pp. 141, 142. 



