94 THE NATURE OF ANIMAL LIGHT 



to the same temperature and then mixing them one can 

 measure any increase or decrease of temperature which 

 occurs during the luminescence which results from mixing. 

 "We can thus gain some idea of the heat of oxidation 

 of luciferin. 



As a determination of heat production is of consider- 

 able interest the method will be given in some detail. 

 Although the experiment sounds very simple, it is actually 

 somewhat difficult to carry out. The attainment of tem- 

 perature equilibrium between two solutions is very slow 

 when one wishes to obtain them to within 0.001 ° C. 

 of the same temperature. After many attempts, the fol- 

 lowing arrangement of apparatus (Fig. 33) was found 

 most satisfactory. About 10 c.c. luciferin solution was 

 placed in the inner tube (D) of a special non-silvered 

 thermos bottle (A). About 1 c.c. of luciferase solution was 

 placed in a very thin-walled glass tube (E) which was 

 immersed in the luciferin 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 (.008 in) — copper (No. 30, B and S, 

 enamel insulated) wire were paraffined and placed in each 

 tube and the copper wires connected through a copper 

 double throw switch (C) with a Leeds and Northrup 

 d'Arsonval wall galvanometer (No. 34637, silver strip 

 suspension) of 35 ohms resistance and 310 megohms sensi- 

 tivity. The constant temperature junctions (N) were 

 placed in a large Dewar flask (D) filled with water at 

 approximately the same temperature as the luciferin 

 solution. One mm. galvanometer scale division repre- 

 sented 0.003° C. and the division readings could be esti- 

 mated to tenths. By means of a glass rod (F) placed in 



