THE CHEMISTRY OF LIGHT PRODUCTION 93 



CO2 is produced to be detected and that this may be due 

 to the buffer action of the luminous substances themselves. 

 After all, unless luminescence is connected with respira- 

 tion, we should hardly expect CO2 to be produced. 



Another method of testing COo production is to meas- 

 ure the amount of heat produced during luminescence. 

 Substances burned during respiration give off consider- 

 able heat, one gram of glucose to COo and HoO, as much as 

 4000 calories. We have seen in Chapter III that no infra- 

 red radiation is produced in the light of the firefly. This 

 does not mean, however, that no heat is produced by the 

 reaction which produces the luminescence. A tempera- 

 ture change of a few thousandths or hundredths of a 

 degree would evolve no measurable radiation. Coblentz 

 (1912) first studied the problem of heat production in 

 the firefly, using a thermo-couple as the measuring instru- 

 ment. He came to the conclusion that the temperature 

 of the insect was slightly lower than the temperature of 

 the air and that the luminous segments were slightly 

 hotter than the non-luminous segments, whereas a dead 

 firefly is of the same temperature as its surroundings. 

 No definite increase or decrease in temperature could be 

 established during the flash of the firefly. However, fur- 

 ther work on the firefly is much to be desired. 



The use of a living animal for such measurements in- 

 troduces 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. Utilization of extracts of luminous 

 animals containing the luciferin and lucif erase mentioned 

 above avoids the complications due to muscular contrac- 

 tion. By bringing the solutions of luciferin and lucif erase 



