OXYGEN AND LUMINESCENCE. 91 



is added the blue color returns and then the cilia begin beating 

 again. 



The luminescence of a mixture of Cypridina luciferin and 

 luciferase is immediately extinguished by hydrosulphite and 

 returns again on shaking with air at a time when methylene 

 blue is just beginning to show a slight blue color. If some dry 

 powdered Cypridinas are added to hydrosulphite sea water, it 

 will be observed that fragments of undissolved luminous material 

 are luminescent but the light disappears very quickly. There is 

 apparently some air entangled, possibly mechanically, with the 

 dry photogenic substances and when this is used up luminescence 

 ceases. I had previously made this observation in another 

 manner (Harvey, 1920). 



In using methylene blue as an indicator, it must be borne in 

 mind that mere removal of oxygen will not reduce methylene 

 blue but that once reduced, a blue color will return when traces 

 of oxygen are present. However, the reoxidation of methylene 

 blue is rather slow except in alkaline solutions. The color 

 change of methylene blue is also affected by light (Clark, 1925). 

 Absence of luminescence in Cypridina luciferin-luciferase or in 

 luminous bacteria can also be used as an indicator of lack of 

 oxygen (the former is more delicate; bacteria begin to luminesce 

 at an oxygen pressure = .0053 mm. Hg) and mere removal of 

 oxygen is sufficient for cessation of luminescence in both cases. 



4. Addition of platinized asbestos to the fluid and passage of 

 hydrogen through it. This affords a quite rapid method of 

 removing oxygen from fluids and the hydrogen need not be 

 absolutely free of oxygen. It is far more rapid than bubbling 

 pure hydrogen through the fluid without platinized asbestos. 

 By pure hydrogen I mean hydrogen that has been passed over 

 platinized asbestos heated to dull redness in a quartz tube. 

 Such hydrogen contains oxygen in equilibrium at io~ 26 atmos- 

 pheres. It must not come in contact with rubber or oxygen 

 will be absorbed from the rubber in sufficient amount to cause 

 luminescence of Cypridina luciferin-luciferase solution. My 

 studies on luminescent solutions have impressed me with the 

 difficulty of removing small amounts of oxygen from fluids and 

 the slowness with which a fluid comes into equilibrium with a 



