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. To prepare the luciferin solution, two grams of dried _Cypridina_ were dissolved in 20 c.c. hot water and 10 c.c. of this 10 per cent. solution was used in the thermos bottle in the above experiments. If we assume that 1 per cent. of the dried _Cypridina_ is luciferin, 0.01 gram of luciferin on oxidation was not able to raise the temperature of the 10 c.c. (in reality 11 c.c., since 1 c.c. luciferase solution was mixed with the 10 c.c. luciferin solution) .001° C. This means that 1 gram luciferin liberates _at least less_ than 10 calories during the luminescence accompanying oxidation.