RHYTHMIC PULSATION 



331 



It is interesting that the temperature of maximum pulsation 

 rate should be so near the temperature, at this time of year, of 

 the sea water in which the animals were living; this was 24° 

 to 27° in the day time. 



V. ACTION OF DEPRESSING AGENTS 



a) Anaesthetics. The effects of typical anaesthetics upon 

 rhythm in the isolated cloaca of Stichopus are illustrated by the 

 following : 



Chloroform 



Experiment 46.1. July 29. Stichopus 7noehii, 21.5 cms. long; before 

 excision of cloaca, 61 seconds for 10 pulsations. 



- Previous tests had shown that transferring the pieces from one solution to 

 another had no effect on pulsation rate, even though during handling the sphincter 

 was closed. 



Ether, ethyl alcohol and ethyl carbamate gave similar results, 

 i.e., the depression of rhythm was, within limits, reversible. 

 Magnesium sulphate to the extent of 0.25 M added to sea water 

 stopped pulsation in about 10 to 12 minutes. Urethane and 

 chloretone were compared quantitatively, with the result that 

 when freshly isolated cloacal pieces were immersed in tt) n chlo- 

 retone in sea water they ceased to pulsate in less than 3 minutes, 

 whereas in 2^0 urethane pulsation lasted for as much as 80 

 minutes. 



