THE EFFECT OF DIFFERENT TEMPERATURES ON THE MEDUSA 



CASSIOPEA, WITH SPECIAL REFERENCE TO THE RATE OF 



CONDUCTION OF THE NERVE IMPULSE. 



BY E. NEWTON HARVEY. 



During the summer of 1909 a partial study was made of the effects 

 of temperature on the nerve and muscle tissues of the scyphomedusa 

 Cassiopea xamachana. The excellence of this jelly-fish for experimental 

 work has already been commented on by several writers. It lives in 

 great numbers in the bottom of the moat surrounding Fort Jefferson, 

 Tortugas. The water in the moat varies in depth from 3 to 5 feet at low 

 tide with a difference between high and low water of less than 3 feet. 

 The temperature of the water at the bottom, where the jelly-fish live, 

 after a 2-days storm, was 27 C. on July 18, 7 a.m., the coolest weather 

 this summer. I think this is the lowest temperature attained in the 

 summer. Next day at i p.m. the temperature had risen to 30, and 

 next day, also at i p.m., it was 29.5. The temperature on the very 

 hottest days was not taken, but I think it may become as high as 32 to 

 33, as the surface-water in the moat on such days is very warm to the 

 touch. The average normal summer temperature of Cassiopea may 

 therefore be placed at about 29. 



Since the temperature to which tropical animals are exposed is so 

 uniform, it is not surprising to find that they are quite sensitive to even 

 slight changes of temperature. However, Cassiopea offers such excep- 

 tional advantages in other respects that the experiments reported below 

 were undertaken, even though the effects of a wide range of temperature 

 could not be investigated. 



I wish to express my sincerest thanks to Dr. Mayer for valuable 

 suggestions and for the many opportunities which he gave me of carry- 

 ing out the work described herein. I am also indebted to Dr. J. H. 

 Hilderbrand, of the University of Pennsylvania, for assistance, especially 

 in calculating the diffusion rates of MgSO 4 and CH 3 COOH. 



The investigations may be arranged under two heads: (i) The 

 temperature limits of activity and thermal death-points of muscle and 

 nerve. (2) The temperature-coefficients of pulsation and nerve con- 

 duction. 



A third series of observations was made on the effects of inhibiting 

 electrolytes at different temperatures, 10 apart. If the ions enter into 

 combination with any substance in the muscle and the cessation of 

 contraction is connected with the formation of some compound, for 

 instance an ion-proteid, then we should expect contraction in the inhibit- 



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