90 THE NATURE OF ANIMAL LIGHT 



oxygen was used up and the bacteria ceased to glow. 

 If now a match was struck for a fraction of a second, 

 sufficient oxygen was formed by photosynthesis to cause 

 the bacteria to luminesce for a short time. 



Exact figures on the minimal concentration of oxygen 

 for luminescence cannot be given. The luminescent secre- 

 tion of Cypridina hilgendorfii will still give off much light 

 if hydrogen containing only 0.4 per cent, of oxygen is 

 bubbled through it, i.e., a partial oxygen pressure of 1/250 

 atmosphere (3.04 mm.Hg). However, addition of a fresh 

 emulsion of yeast cells to a glowing Cypridina secretion 

 is sufficient to rapidly extinguish the light, because the 

 yeast is capable of utilizing the last trace of oxygen in the 

 mixture. Light only appears when, by agitation, we cause 

 more air to dissolve. The minimal concentration of oxy- 

 gen for luminescence of Cypridina lies somewhere between 

 3.04 mm. and the amount which living yeast fails to 

 extract from solution, a concentration approaching zero. 

 It is probably nearer the latter figure. 



As the oxygen pressure is increased from to about 

 7 mm., the intensity of the Cypridina luminescence in- 

 creases and at the latter figure the light is just as bright 

 as if the solution were saturated with air (152 mm.02). 

 Thus, the luminescence requires only a low pressure ©f 

 oxygen and the similarity to the saturation of haemoglobin 

 with oxygen is obvious. Just as haemoglobia is nearly 

 saturated with oxygen at low pressures and becomes 

 bright red in color, so the luminous material be- 

 comes saturated with oxygen at low pressures and 

 glows intensely. 



Boyle also made many experiments to show that air 

 was necesary for the life of animals and the germination 



