244 Papers from the Department of Marine Biology. 



and in solutions weaker than m/2000 there is no effect on luminescence. 

 It is of interest to note the slight effect of KCN on oxidations connected 

 with luminescence in comparison with its marked inhibiting effect on 

 oxidations by plant oxidases and on the oxygen consumption of egg- 

 cells and other animal tissues (Loeb and Wasteneys, 1913). The 

 oxidations connected with light-production are apparently entirely 

 different from those concerned with cell-respiration. 



ABSENCE OF OXYGEN. 



The effect of the lack of oxygen on Noctiluca was tested by subjecting 

 the animals to an atmosphere of bubbling well-washed hydrogen from 

 a Kipp generator. When thus treated, the luminescence gradually 

 grows fainter for an hour until it is very faint. If air is now admitted 

 to the tube, the animals respond on irritation as normally and just as 

 brilliantly. Animals caught by the surface film of water on the sides 

 of the tube give light when oxygen is admitted, even without mechanical 

 stimulation. The mere admission of oxygen after its absence may 

 therefore serve as a stimulus. 



If the animals are kept for 2 hours, however, in the bubbling hydro- 

 gen, the luminescence goes out entirely and does not return on admit- 

 ting air to the tube, the animals having probably been killed by the 

 treatment. In a control experiment, hydrogen was bubbled through a 

 tube containing the animals, in presence of oxygen; the animals were 

 normal after 1 hour, but gave no response after 2 hours. It is therefore 

 the mechanical disturbance and not the lack of oxygen which is fatal to 

 the animals subjected for 2 hours to the hydrogen. 



Light-production in Noctiluca is therefore dependent upon a supply 

 of oxygen, as is to be expected. Since the cells deprived of oxygen 

 immediately give light on admitting oxygen, even without stimulation, 

 they must be permeable to oxygen at any tune, and not merely upon 

 stimulation and death, when light-production ordinarily takes place. 

 That oxygen is necessary for light-production in Noctiluca is contrary 

 to the ideas of Quatrefages (1850), and brings this animal in line with 

 all the other light-producing animals in which the question has been 

 carefully investigated. 



TEMPERATURE. 



With increase of temperature up to 42 or 43 C., noctilucas give a 

 normal response. From this point to 48 or 49, a steady glow is given 

 and then the light goes out completely and there is no recovery if 

 cooled immediately. With decrease in temperature, the animals flash 

 more than normally until the temperature reaches 5 to 0, when they 

 give a constant glow. If kept only a few minutes at 0, they will 

 recover on warming and again give a normal response; but if kept at 

 for 15 minutes they do not recover. 



