THE CHEMISTRY OF LIGHT PRODUCTION 89 



It should be clearly borne in mii^d that if we place lumi- 

 nous organisms, say bacteria or fungi, in an atmosphere 

 devoid of oxygen and find that no light is produced, this 

 may merely mean that certain functions of the cell are 

 interfered with, including light production, but does not 

 necessarily indicate that oxygen is actually used up in 

 the photogenic process; If we find, however, that ex- 

 tracts of luminous cells or luminous secretions devoid of 

 cells cease to light when the oxygen is removed and again 

 luminesce when it is returned, we may be quite certain 

 that the photogenic process itself requires free oxygen. 

 As luminous extracts of fireflies, pennatulids, ostracods, 

 Pholas and others give off no light when the oxygen ia 

 removed, we may safely conclude that for these lumines- 

 cences, oxygen is necessary. Bacteria, fungi, and Nocti- 

 luca, whose light also disappears in absence of oxygen, 

 although they are whole cells, we may by analogy also 

 assume to require oxygen in the photogenic processy "^ 



Some of the earlier workers on fireflies and Tfoctiluca 

 obtained light even after placing these organisms in ab- 

 sence of oxygen, but they did not realize how low is the 

 amount of oxygen necessary to produce light. It is diffi- 

 cult to remove traces of oxygen from the water, traces 

 which are nevertheless sufficient to cause luminescence. 

 If the organisms are numerous, as in an emulsion of 

 luminous bacteria, they will themselves use up all the 

 pxygen and the liquid soon ceases' to glow except at the 

 surface in contact with air. We may gain an idea of the 

 amount of oxygen necessary for luminescence from an 

 experiment of Beiierinck (1902). He mixed luminous 

 bacteria with an emulsion of clover leaves containing 

 chloroplasts and kept the two in the dark until all the 



