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 time, 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.