The Depolarizing Nature of the Trigger 31 



associated with the latter neuron is of the tonic type, which 

 develops and loses tension much more gradually than the twitch- 

 type one. Much of the experimental work described below was 

 obtained from the slowly-adapting neuron, since the state of 

 excitation of this cell remains relatively constant and the mechanical 

 threshold for impulse initiation is usually lower than that of the 

 fast-adapting cell. Changes in effective stimulus strength can 

 thus be performed with much smaller manipulations of the 

 preparation. The latter feature confers considerable advantage, 

 because of the critical geometrical relationship which exists 

 between the impaled neuron and the comparatively rigid glass 

 recording micropipette. 



The records in figures ii and 12, which have now become 



Fig. II. Intracellular recordings from crustacean abdominal 

 stretch receptor neurons. (A) Slowly-adapting neuron; onset 

 and cessation of stretch indicated by arrows. (C) Rapidly-adapting 

 cell. (B) Extracellular records from a slowly-adapting neuron 

 which had been treated with o-i per cent novocaine. Voltage 

 calibration the same for (A) and (C). Horizontal bars all indicate 

 one second. (From Eyzaguirre and Kuffler,*' Fig. 3.) 



