PANUS STYPTICUS LUMINESCENS 399 



re-enter the end of the tube.^ This perfect control of the fungus 

 light, made possible by removing air from the fruit-bodies or restoring 

 it to them, and actually effected by the operation of the taps d 

 and i and the stopper h, finds an analogy in the control of electric 

 light by turning a switch off and on. 



The fact that one can turn the light of the fruit-bodies on or 

 off practically instantaneously by supplying or withholding oxygen 

 proves conclusively that in Panus styjJt. lutninescens the photogen 

 is absolutely dependent for its light-giving power on the presence of 

 oxygen. There can be no doubt, therefore, that here, as in other 

 luminous organisms, the emission of light is an oxidative process. 

 The oxidative process, however, as indicated by the investigations 

 made upon it by animal biologists, is in all probability quite distinct 

 from the oxidative process that is associated with respiration.^ 



A Kipp apparatus generating carbon dioxide was substituted for 

 the Kipp apparatus generating hydrogen in the apparatus shown in 

 Fig. 172, and a series of experiments like those just described was 

 then made. When the air surrounding the luminous fruit-bodies 

 was replaced by carbon dioxide, the light immediately grew dim, 

 and it ceased to be emitted within about three seconds. When, 

 by pulling out the stopper h, air was allowed to re-enter the 

 experimental tube, the fruit-bodies immediately became luminous 

 and within about one second regained their normal intensity of 

 luminescence. 



Some pure nitrogen was prepared by slowly bubbling air through 

 a strong solution of ammonia and then passing it over copper 

 turnings heated to redness. The nitrogen was collected by siphoning 

 it into a two-litre bottle which was first filled with water acidulated 

 with sulphuric acid. When about a litre of nitrogen had been 

 collected, the intake pipe was carefully washed with dilute sulphuric 

 acid to remove the last traces of ammonia. The nitrogen-gas bottle, 

 together with the siphon and water-bottle, was then attached to 



1 Had the experimental tube e been much shorter, say 1 -5 inches long instead of 

 7 inches, the hydrogen, when allowed to flow, would certainly have replaced the air 

 in the tube much more rapidly; and then, no doubt, the disappearance of the fungus 

 light would have taken place in much less than three seconds — perhaps in less than 

 one second. This variation in the experiment, however, was not tried. 



2 Vide, E. N. Harvey, loc. cit., pp. 99-100. 



