[Illustration: FIG. 33.--Apparatus for determining heat production during luminescence of luciferin. A, special thermos tube. B, Dewar flask for constant temperature junctions. C, double throw switch. D, tube containing luciferin solution. E, tube containing luciferase solution. F, glass rod for breaking E. G, rubber stopper with groove, K, for pulley cord. H, cork closing thermos tube. J, brass sleeve in H allowing rotation of E. L, thermojunction in luciferase solution. M, thermojunction in luciferin solution. N, constant temperature junctions.]
[Illustration: FIG. 34.--Curve showing temperature change when two tubes containing water at the same temperature are mixed. 0.1 galvanometer scale division = 0.003° C. Dots represent readings of thermocouple in tube D; crosses readings of thermocouple in tube E.]
It was found that even after the luciferase and luciferin solutions came to the same temperature within the thermos bottle, this was not necessarily the same as that of the room and a slow rise or fall occurred as indicated by a slow drift of the galvanometer coil. Readings of each thermocouple on the galvanometer scale were therefore taken at one-minute intervals for some time before and after mixing the luciferin and luciferase solutions and plotted as curves. Control experiments were also carried out in exactly the same manner as the luciferin-luciferase experiments, but water was placed in the two tubes instead of luciferin and luciferase. Figs. 34 and 35 give typical experiments with water and with luminescent solutions, respectively.
[Illustration: FIG. 35.--Curve showing temperature change when luciferin and luciferase solutions at the same temperature are mixed. 0.1 galvanometer scale division = 0.003° C. Dots represent readings of thermocouple in luciferin solution; crosses, readings of thermocouple in luciferase solution.]
With both control (water) and luciferin experiments there was a slight rise in temperature on mixing the liquids in the two tubes. The average rise of five control (water) experiments was .0054° C. and the average rise of five luciferin experiments was .0048° C.
The average rise in temperature is no doubt due to heat from friction in mixing of the liquids and breaking of the glass tube. The difference in the average rise of control and of luciferin experiments is so small (.0006° C.) as to have little significance. We may therefore conclude that if any temperature change occurs during the luminescent reaction it is certainly less than 0.001° C. and probably less than 0.0005° C., too small to be measured by this method.