200 Journal of Comparative Neurology and Psychology. 



Rhythmical Pulsation in Animals. By Alfred G. Mayer. 



Experiments made at the Tortugas Marine Laboratory of the Carnegie Insti- 

 tution upon Cassiopea, Salpa, Lepas, and the loggerhead turtle give results as 

 follows: 



Rhythmical pulsation can be sustained only when a strong stimulus is counter- 

 acted by an inhibitor, so that the pulsating organism is maintained at or near the 

 threshold of stimulation, in a state analogous to that of unstable equilibrium, thus 

 allowing weak internal stimuli to produce recurrent movement. 



In the lower marine animals the NaCl, calcium, and potassium of the sea-water 

 combine to form a powerful stimulant, which if unchecked would produce only 

 sustained tetanus, but the magnesium overcomes this effect by its anesthetic 

 (diastolic) influence. 



The pulsating organs of terrestrial animals are also stimulated by optimum 

 combinations of NaCl, with potassium and calcium, and this is held in check by a 

 definite proportion of magnesium. 



A Ringer's solution resembles this optimum combination of NaCl, calcium and 

 potassium, and is only a stimulant, not an inorganic food. It must be counter- 

 balanced by magnesium in order to enable it to sustain pulsation indefinitely. 



In Cassiopea any paralyzed strip of sub-umbrella tissue, cut in the shape of a 

 closed circuit, will remain indefinitely in rhythmical pulsation, if once a contraction 

 wave be started in the circuit. Everytime this wave returns through the circuit of 

 tissue to the place whence it started, it is re-stimulated and sent forth anew, and 

 being thus reinforced at each r-eturn it is sustained indefinitely. 



In the scyphomedusa, Cassiopea, the diffuse nervous or epithelial elements of 

 the sub umbrella transmit the pulsation stimulus to which the muscles respond by 

 contraction. 



The peripheral muscular layer of the wall of the loggerhead turtle's heart is the 

 only part actively concerned in the rhythmical movement, and the internal cavernated 

 mass of the heart's tissue may be removed without checking the pulsation. This 

 peripheral part of the muscular wall of the heart tends to maintain itself in pulsa- 

 tion very much as will circuits made of the sub-umbrella tissue of Cassiopea. 



The pulsation-stimulus acts solely upon the peripheral muscular layer of the 

 heart's wall, the inner cavernated tissue remaining passive. 



The above is a brief review of Publication No. 47, of the Carnegie Institution 

 of Washington, "Rhythmical Pulsation in Scyphomedusae," igo6. 



