Summary.
1. The specific gravity of Noctiluca is less than that of sea-water, so that normally the animals float at the surface. Since they contain no air-bubbles or large oil-drops, their lower specific gravity must be due to a lower salt-content than that of sew-water. When placed in a mixture of 4 sea-water to 6 fresh-water, the animals sink, their salt content being now greater than that of the surrounding medium, but later they rise to the surface, a process independent of the movement of the tentacle. They therefore absorb water until their salt-content is again less than the medium, thus reestablishing their normal relation to the surrounding medium. This water must be absorbed against the osmotic pressure of the salts of sea-water, a process contrary to physical laws. The animals can not only lessen their specific gravity, but can also increase it, as shown by the fact that they sink to the bottom of the sea on windy days. Anesthetics, acids and alkalies, KCN, and the pure salts of sea-water do not interfere with this regu latory mechanism, except when they cause irreversible changes and death; dead noctilucas always sink to the bottom.
2. Light-production in Noctiluca normally occurs only on stimulation of any kind, and is a momentary bright flash. The only other light response is a steady glow occurring before death and under many experimental conditions—e. g., diluting with fresh-water, addition of acids and alkalies, KCN, cold (5° to 0° C.), heat (43° to 49° C.), anesthetics, and a constant galvanic electric current.
3. In very dilute sea-water (3 sea-water to 7 fresh-water down to pure fresh-water) the animals give a constant glow for a few minutes and then die. If the sea-water is diluted with isotonic cane-sugar instead of water, a normal response is given even with 1 sea-water to 9 cane-sugar. But in isotonic cane-sugar alone a normal response is given for only a short period, followed by a steady glow and death, showing that the animals must be bathed by a medium of minimal salt-content as well as of definite osmotic pressure.
4. The normal light-response of Noctiluca is dependent on the balanced salts of sea-water. Isotonic Na, K, Ca, and Mg are all toxic if alone in solution.
5. n/2000 HC1 and n/4000 benzoic acid in neutral artificial sea water cause a steady glow for 20 minutes; n/2000 and n/500 NaOH give a steady glow for 6 and 30 minutes respectively. In NaOH the luminescence stops before the penetration of the alkali, and in after the penetration, as indicated by the color-change of animals stained in neutral red.
6. KCN has little effect on light-production in relatively strong concentrations. Animals in n/250 KCN respond normally for 30
minutes and then give a steady glow for 35 minutes.
7. Oxygen is necessary for light-production. Animals deprived of oxygen immediately glow on the admission of oxygen even without stimulation.
8. When the temperature is gradually raised, a steady glow appears at 42° C. and stops at 48°, when the animals die. When the tempera ture is lowered a steady glow appears at 5° and continues to The animals will recover on warming if kept for only a few minutes at 0°.
9. Centrifuging has no effect on the luminous response, although the protoplasm is thrown to whatever part of the cell happens to be away from the axis of the centrifuge. On standing, the protoplasm returns to its normal position under the tentacle.
10. With a constant galvanic current noctilucas flash at the make, stay glowing during the passage of the current, and stop glowing at the break with no flash. Animals will respond normally to mechanical stimulation during the passage of the current. The luminescence is uniform throughout the organisms, no polar effects being observed. Induced shocks call forth the usual flash caused by stimulation. The animals fatigue readily with interrupted induced shocks.
11. Noctilucas injured by puncturing with a needle or by a strong induced current respond to mechanical or electrical stimulation. If completely broken to pieces by pressing through cheese-cloth, the filtrate gives a constant glow, but there is no flashing on stimulation.
12. The luminescence is traceable to points of light coming from granules (photogenin) in the protoplasm. No photophelein could be demonstrated.
13. Noctilucas may be anesthetized by m/8 ether, 1/3 saturated chloroform, 1/16 saturated thymol, 1/8 saturated chloretone, m ethyl and m/8 butyl alcohol, so that they fail to give a flash on stimulation, but they always give a very faint glow; this disappears and the normal response returns on removing the anesthetic. Light-production is dependent on the consumption of oxygen. Whether the anesthesia of luminous cells is due to the fact that oxygen can not pass through the membrane, or to the fact that it can not be used, was tested by an experiment in which the cell-substance of anesthetized cells was per mitted to come into contact with dissolved oxygen. Narcotized cells were broken up by shaking with sand and it was found that they pro duced only a faint light, whereas normal cells so treated became very brilliant. The anesthetic must therefore attack the mechanism of the utilization of oxygen in the cell, and not the permeability of the cell membrane for oxygen.