Part 12 (1/2)

The effect of temperature on _Cypridina_ luminescence also bears out the preceding conclusions. For a given mixture of luciferin and luciferase the light becomes more intense with increasing temperature up to a definite optimum and then diminishes in intensity. The diminution in intensity above the optimum is due to a reversible change in the luciferase so that its active ma.s.s diminishes. This change becomes irreversible in the neighborhood of 70 (depending on various conditions), where coagulation of luciferase occurs. Light will appear at 0 but it is far less intense than light at higher temperatures and it is more yellow in color. The light of optimum temperatures is quite blue. The weaker light at temperatures above the optimum is also more yellow in color. I believe this difference in color is a function of the slowed reaction velocity, for a mixture of luciferin and luciferase which gives a bluish luminescence at room temperature, will give a weaker and yellowish luminescence if diluted with water. Dilution with water will slow the reaction velocity. If the difference in color were not real but due to change in color sensitivity of the eye with different intensities of such relatively weak light (Purkinje phenomenon), the weaker light should appear more blue. As the weaker light appears more yellow, I therefore believe the color difference is actual and not subjective.

A minimum, optimum, and maximum temperature for luminescence is observed in all luminous organisms. The minimum is usually very low. Luminous bacteria will still light at -11.5 C. The power to luminesce under ordinary conditions is not destroyed by exposure to liquid air, for, on raising the temperature, light again appears (Macfayden, 1900, 1902).

Almost all organisms will luminesce at 0 C., and the luminescence minimum probably represents the point at which complete freezing of the luminous solution occurs. It is very low with bacteria because they are solutions in capillary s.p.a.ces of very small size, a condition tending to lower the freezing point.

The luminescence maximum represents the point at which luciferase is reversibly changed so as to be no longer active. If the temperature is again lowered the luciferase again becomes active and light reappears.

Some degrees above this, and in all forms well below the boiling point, luciferase is coagulated and destroyed. As the coagulation point of proteins depends on many factors, such as time of heating, salt content, acidity, etc., so the luciferases of different animals coagulate at different temperatures depending on these conditions. Some of the more reliable observations on these critical temperatures are collected in Table 14.

TABLE 14

_Temperature Limits of Luminescence for Luminous Organism_

-------------------------+---------------------+-------+-------+-------+ Organism

Author and date

Minimum

Optimum

Maximum

-------------------------+---------------------+-------+-------+-------+ Pseudomonas javanica

Eijkman, 1892

-20

25-33

45

Bacterium phosph.o.r.escens

Lehmann, 1889

-12

...

39.5

Bacterium phosph.o.r.eum

Molish, 1904, book

-5

16-18

28

Light bacteria

Tarchanoff, 1902

-7

15-25

37

Light bacteria

Harvey, E. N., 1913

-11.5

15-20

38

Mycelium X

Molish, 1904

...

15-25

36

Lampyrids

Macaire, 1821

-10

33

46-50

Pyrophorus noctilucus

Dubois, 1886

...

20-25

47

Photuris pennsylvanica