252 Papers from the Department of Marine Biology. 



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. (/., diluting with fresh- water, addition of 

 acids and alkalies, KCN, cold (5 to 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 NHjOH 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 NH 4 OH 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 0. 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. 



