503 



The Time taken in passing the Synapse in the Spinal Cord of 



the Frog. 



By Florence Buchanan, D.Sc., Fellow of University College, London. 



(Communicated by Professor Sherrington, LL.D., F.K.S. Eeceived 



March 1, 1907.) 



(Abstract.)* 



The time taken by an impulse to cross a single synapse has been estimated 

 by the measurement and comparison of cord-delays in different reflexes of 

 the decerebrate frog. The cord-delay was determined by measuring, (1) the 

 interval of time which elapsed between the moment of application of a single 

 break induction shock to a nerve containing afferent (sensory) fibres and the 

 moment of appearance in a particular spot of a particular muscle of a 

 response, known to have no latency of its own (the electrical response), and 

 shown to have been produced by the excitation of the afferent fibres ; by 

 then measuring and deducting from this time-interval, (2) that which elapsed 

 before a response occurred in the same spot of muscle when the same or a 

 similar induction shock was applied to the efferent (motor) fibres of the 

 nerve supplying it. From the remainder the time was deducted which would 

 be taken by an impulse travelling at the rate of 30 metres per second to 

 traverse the measured length of nerve between the two points of excitation. 



The recording of the intervals was automatic, the movements of the 

 meniscus of the capillary electrometer, the two terminals of which were 

 connected with the muscle, being photographed on plates moving at known 

 rates. The recording muscle chosen was the gastrocnemius, and the nerves 

 stimulated were the sciatics of the same and of the opposite side. The 

 experiments were all made on autumn or winter frogs. 



It was found that a single induction shock was only capable of producing 

 a true reflex response in the gastrocnemius from a normal cord when applied 

 to the sciatic of the same side. The same stimulus applied to the opposite 

 sciatic only produced the response when the excitability of the cord had 

 been raised by some drug. The drugs used for the purpose were strychnine 

 and phenol. 



When the same-side sciatic was stimulated, the reflex response in the 

 muscle was quite distinct from the response produced directly by the excita- 



* The paper will be published in full in the first number of the Physiological Part of 

 what was the 'Journal of Anatomy and Physiology,' to appear in January, 1908, edited 

 by Professor Schafer, F.K.S. 



