36 



Papers from the Marine Biological Laboratory at Tortugas. 



one dish of sea-water to another slows the conduction while in the air, 

 but nearly the original rate is regained again in sea-water. A more 

 favorable object for the study of nerve conduction could not be desired. 

 For the following experiments ring-shaped pieces of tissue, without 

 sense-organs, are cut from the disk, as has been described by Mayer.' 

 If these are stimulated strongly at one point (S) by induced shocks, a 

 nerve impulse passes around each side of the ring and the two block 

 on the opposite side (fig. 3). If one impulse is itself blocked (fig. 4) by 



Fig. 4. 



pressing on the nerves, for a moment, with a glass rod near the point 

 of stimulation, the impulse of the opposite side will travel around the 

 ring (stimulating the muscles as it goes) indefinitely, since it meets no 

 counter impulse to stop it. Mayer has recorded rings of Cassiopea started 

 in this way conducting for several days with a practically constant rate. 



Below 18° it was found difficult to start impulses that would keep 

 going. Even when the ring was first cooled and then stimulated, the 

 impulse stopped suddenly after a few seconds. Between 18° to 38°, 

 however, an accurate temperature conduction rate curve could be plotted. 

 All the readings on curve A (fig. 5) have been obtained from one ring 

 which was started at 17° and then gradually warmed at an average rate 

 of 1.0° in 4 minutes. 



Temperatures are plotted as abscissse; conduction rate {i.e., the 

 number of times per minute the nerve impulse passes around the ring 

 of tissue) as ordinates. The outside diameter of the ring was 104 mm. 

 and its inside diameter 61 mm. The following table gives actual veloci- 

 ties of propagation for a few temperatures in millimeters per second: 



It is interesting to note that the conduction wave, to pass around 

 the ring regularly, must move much more rapidly on the outer than the 

 inner side. There is apparently some coordinating mechanism regulat- 

 ing the velocity of the impulse in different regions of the subumbrella. 

 If a conducting ring be cut in two the original velocity is not maintained 

 in each new ring, i.e., the new rings do not remain synchronous. 



' Carnegie Institution of Washington, Pub. No. 102, p. 117. 



