E. NEWTON HARVEY 271 



riety of substances, it loses strength during the process and the crude 

 luciferase solution is the most powerful that can be obtained. 



A similar extract may be prepared with hot distilled water which 

 contains one of the photogenic substances, luciferin, all of the pro- 

 teins of the animal not coagulated by heating, the remaining salts, and 

 other material soluble in hot water. My procedure is to add boiling 

 water directly to the dry powder, boil about 20 seconds, and filter 

 quickly while hot. The filtrate is slightly opalescent, yellow colored, 

 and does not darken on standing. On cooling, this solution often 

 glows faintly but if heated to the boiling point a second time the glow 

 ceases and does not return on cooling. However, its content of 

 luciferin is diminished because some has oxidized to oxyluciferin. 

 This hot water extract of CypridincE will be spoken of as crude lucif- 

 erin solution. It gives a bright light with luciferase. 



If the hot water extract stands in a shallow dish at room tempera- 

 ture, the luciferin disappears completely in the course of some hours, 

 the time depending on its concentration. This is due to oxidation 

 of the luciferin apart from luciferase, as may be easily determined by 

 keeping the luciferin extract in absence of oxygen. I have kept such 

 a solution for 90 days in a test-tube covered with a layer of vaseline 

 1 inch in depth to prevent access of air, and at the end of that time 

 it was capable of giving a brilliant light when mixed with luciferase. 

 Luciferin and luciferase together in solution are likewise both stable 

 in the absence of oxygen. I have kept such solutions in an evacu- 

 ated tube or in a hydrogen atmosphere for many months and at the 

 end of that time on admitting air a brilliant light appears. 



The oxidative disappearance of luciferin, like other chemical reac- 

 tions, is greatly accelerated at the higher temperatures. In a previous 

 paper^ I called attention to the fact that whereas luciferin was not 

 destroyed by a short boiling, 3 or 4 minutes boiling were sufficient to 

 destroy it. This is entirely a matter of the increased rate of oxidation 

 at the boiling point. We can boil a solution of luciferin without harm 

 for 30 minutes provided the boiling is carried out in a stream of hy- 

 drogen which has been rendered free of oxygen by passage over a 

 glowing platinum spiral. Acid retards and alkali favors the oxida- 

 tion of the luciferin (apart from luciferase). A solution of luciferin 

 made slightly acid with HCl may be boiled for 25 minutes in the air 



