34 Papers from the Marine Biological Laboratory at Tortugas. 



between a heart and a medusa is very close, the temperature limits of 

 an invertebrate heart have been selected. 



Carlson ^ gives the following temperatures at which activity ceases 

 in the heart of Limulus from the region of Woods Hole. The effect of 

 temperature on the heart ganglion, muscle, and nerves can be readily 

 studied separately in this form: 



{Contractions cease o to — i° C. 

 OPH""""^ iotoi4° 

 Contractions cease 32° 

 Tonus or heat rigor 47 to 50° 



(Stimuli cease o to — 1 ° C. 

 Stimuli cease 42° 

 Ganglion killed Above 47 to 50° 



(Conduction ceases — 2° C. 

 Conduction ceases 43° 

 Nerves killed Above 47° 



It will be noticed that, although the normal temperatures of the 

 two animals are very different (more than 10°) yet their upper temper- 

 ature limits are nearly the same. Cassiopea is an animal living constantly 

 within about 15° of its death-point, yet is not adapted to withstand higher 

 temperatures than the heart of a northern animal living 25° to 30° 

 from its death-point. The Limulus heart can withstand much lower 

 temperatures than Cassiopea, however. This is what we might expect. 



It would be interesting to determine the temperature limits for the 

 heart of the Limulus which occurs around the Marquesas Keys, near 

 Tortugas, and whose normal temperature is very different from that of 

 the Limulus on which Carlson worked. 



THE TEMPERATURE-COEFFICIENTS OF PULSATION AND NERVE 



CONDUCTION. 



PULSATION. 



Cassiopea is not a favorable object for a study of the influence of 

 temperature on pulsation, because it is so readily excited to rapid beat- 

 ing, by handling, by currents of water, and by sudden though slight 

 changes in temperature, both higher and lower than the normal summer 

 temperature (29°). After some time this initial excitation caused by 

 a change in temperature passes off and the beats become fairly constant. 

 On account of the difficulty of obtaining and keeping ice at Tortugas, 

 only a few observations on the pulsation rate were made. 



An average of 6 counts gave the following as the number of pulsa- 

 tions per minute for 4 temperatures: 30°, — 33 per minute: 25°, — 26 per 

 minute ; 20°, — 17 per minute ; 1 6°, — 8 per minute. 



Q,, (2o°-3o°)=ca.2 Q,, (i6°-25°)=3 



The coefficient is of the same magnitude as that for the increase in 

 the velocity of chemical reactions per 10° rise in temperature. All 



'Carlson, Am. Jovirn. Physiol., 15, p. 215, 1906. 



