138 STUDIES ON BIOLUMINESCENCE. XI 



nous segments. No definite increase or decrease in temperature could 

 be established during the flash of the firefly. However, further 

 work on the firefly is much to be desired. 



The use of a Hving animal for such measurements introduces a 

 possible source of error, in that any contraction of the muscles of 

 the animal will produce heat which may add to an increase, or mask 

 a decrease of temperature during luminescence. Utihzation of ex- 

 tracts of luminous animals avoids the compHcations due to muscular 

 contraction. From Cypridina hilgendorfii, a small crustacean, may 

 be prepared a solution of luciferin, an oxidizable substance, and a 

 solution of luciferase, a catalyzer which accelerates the oxidation of 

 luciferin with light production. By bringing the solutions of luciferin 

 and luciferase to the same temperature and then mixing them, one 

 can measure any increase or decrease of temperature which occurs 

 during the luminescence resulting from mixing. We can thus gain 

 some idea of the heat of oxidation of luciferin. 



Although the experiment sounds very simple it is actually some- 

 what difficult to carry out. The attainment of temperature equihb- 

 rium between two solutions is very slow when one wishes to obtain 

 it to within 0.001°C. of the same temperature. After many attempts, 

 the following arrangement of apparatus (Fig. 1) was found most 

 satisfactory. About 10 cc. of luciferin solution were placed in the 

 inner tube (D) of a special non-silvered thermos bottle (A). About 

 1 cc. of luciferase solution was placed in a very thin-walled glass 

 tube (E) which was immersed in the luciferase solution and connected 

 with a small motor so that it could be slowly but constantly rotated, 

 thus stirring the solutions. Thermo-couples (L and M) of advance 

 (0.008 inch) copper (No. 30, B and S enamel-insulated) wire were paraf- 

 fined and placed in each tube and the copper wires connected through 

 a copper double throw switch (C) with a Leeds and Northrup d'Arson- 

 val wall galvanometer (No. 34,637, silver strip suspension) of 35 ohms 

 resistance and 310 megohms sensitivity. The constant temperature 

 junctions (N) were placed in a large Dewar flask (B) and filled with 

 water at approximately the same temperature as the luciferin solu- 

 tion. 1 mm. galvanometer scale division represented 0.003°C. and 

 the division readings could be estimated to tenths. By means of 

 a glass rod (F) placed in the tube containing luciferase solution, 



