Discussion 



Dr. Harvey: For many years I have felt that records of the luminous 

 response of a unicellular organism such as Noctiluca would be of 

 great interest and value for comparison with single muscle fiber 

 contractions or nerve cell potential changes. A graduate student, Mr. 

 J. J. Chang, and I endeavored to obtain and culture Noctiluca for 

 this purpose but without success, and therefore turned to the cteno- 

 phore, Mnemiopsis leicleiji, common at the Marine Biological Labora- 

 tory, Woods Hole. Luminescence appears from a group of cells within 

 the radial canals. Last summer Mr. Chang made an exhaustive study 

 of this luminous response to mechanical stimulation and electrical 

 stimuli of various frequencies. The luminescence intensity was re- 

 corded by photomultiplier tube, amplifier, cathode-ray oscillograph, 

 and camera. The relationship between light emission and strength and 

 duration of stimulus, repetitive stimuli, and fatigue at different tem- 

 peratures has been particularly studied. 



The most interesting result is the almost exact parallel between a 

 luminous response and a muscle contraction. At 21° to 23° C with 

 single square-wave stimulation and a small piece of luminous tissue, 

 a single flash appears having a latent period that varies considerably, 

 a half-rise time of 35, a maximum-peak time of 60, a half-decay time 

 of 48, and a 0.9-decay time of 114 milliseconds. Lowering the tempera- 

 ture prolongs the time course of single flashes, especially the decay 

 phase. Raising the temperature has the opposite effect. Light inten- 

 sity increases as strength of stimulus increases, and repetitive stimuli 

 elicit responses similar to summation of twitches, treppe, incomplete 

 and complete tetanus of muscle. Fatigue appears soon and is a marked 

 characteristic of the luminescent response. Repetitive flashes after a 

 single stimulus have been observed in large pieces of tissue. The 

 conduction rate of a luminous excitation along the canals averages 

 14 cm/sec. Bursts of action potentials, simultaneous with the lumines- 

 cent responses, appear. An abstract of the work has appeared in 

 Science (119, 581, 1954) and the complete paper in the Journal of 

 Cellular and Comparative Physiology. Thus another organism in which 

 the time relations of a luminous response are now well known can be 

 added to those enumerated by Dr. Nicol. 



Dr. Mason: It is well known that the superficial colors of many 

 organisms are under hormonal control. In one type of control of this 



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