156 THE NATURE OF ANIMALJLIGHT 



luciferin give a bright flash of light which disappears 

 ahnost instantly. Concentrated luciferase and concen- 

 trated luciferin give a brilliant light which lasts for an 

 intermediate length of time and weak luciferin and weak 

 luciferase give a faint luminescence which lasts for an 

 intermediate length of time. 



These facts can all be explained by regarding lucife- 

 rase as a catalyzer which accelerates the oxidation of lucif- 

 erin and by assuming that intensity of luminescence is 

 dependent on reaction velocity, i.e., on rate of oxidation. 

 Contrary to the condition for phosphorus and for pyro- 

 gallol there appears to be no optimum concentration of 

 luciferase or luciferin, but the luminescence intensity 

 increases gradually with increasing concentration of lumi- 

 nous substances up to the point where pure (f) luciferin 

 and pure (?) luciferase, as secreted from the gland cells 

 of the animal, come in contact with each other. This, the 

 maximum brightness, is not to be compared with the light 

 of an incandescent solid, but is nevertheless visible in a 

 well-lighted room, out of direct sunlight. 



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 opti- 

 mum 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 mass 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 



