272 STUDIES ON BIOLUMINESCENCE. IX 



without complete oxidation, whereas a neutral or slightly alkaline 

 solution is quickly oxidized. A solution of luciferin will keep very 

 well in a tall test-tube if the tube is left undisturbed. Diffusion of 

 oxygen into the depths of the tube is very slow. Perhaps the best way 

 to obtain a concentrated solution of luciferin is to filter the hot water 

 extract of Cypridina directly into a tall narrow vessel and pass a cur- 

 rent of CO2 through it while cooling. The slight acidity and the 

 anaerobic conditions both prevent oxidation. A little dilute acetic 

 acid may be used in place of carbon dioxide. 



Although both luciferin and oxyluciferin will pass collodion or parch- 

 ment membranes, I have been unable to obtain them in crystalline 

 form, and presume that they also are present in the colloidal state.^ 

 The properties of the luciferin in the hot water extract and the lucif- 

 erase in the cold water extract will be considered under the following 

 heads: Action of enzymes, salting out, alcohol and acetone, solu- 

 bility in organic solvents, alkaloidal reagents, heavy metal salts, 

 acids and alkalies, adsorbents. 



Action of Enzymes. 



Table I gives the results of enzyme experiments. A solution of 

 crude luciferase (or crude luciferin) was mixed with the enzyme 

 preparation and kept at 38°C. in an incubator for from 18 hours to 

 4 days. Controls were always employed, using previously boiled 

 enzyme solution. Experiments were also made to determiaie whether 

 the particular enzyme preparation was active on its substrate, and no 

 experiments were considered in which this was found not to be the 

 case. After the enzyme solution had acted for the proper length of 

 time on the photogenic substances, their light-giving power was tested 

 by adding an equal amount of luciferin (or luciferase) to both con- 

 trol and active tube and comparing the brightness of the light re- 

 sulting from the active tube with that of the control. In order to 

 prevent oxidation the digests of luciferin were carried out in long 

 test-tubes, full of solution, which were either corked or covered with a 



^ Dubois regards Pholas luciferin as a natural albumin and Pholas luciferase as 

 an oxidizing enzyme made up of iron associated with a protein. Dubois, R., La 

 vie et la lumiere, Paris, 1914. 



