12 



Buchanan 



[The first record was taken with the right gastrocnemius to excitation of 

 rio-ht sciatic. The rest were taken with the left gastrocnemius to excitation 

 of left sciatic. No reflex response was obtained when the strength of the 

 current was 1000 units.] 



In three other preparations the variation in the interval was slightly 

 greater, but hardly exceeded Itr. There were, however, three experiments 

 (in two of which four reflex responses, in the third nine, were recorded) in 

 which the shortest and the longest interval on the diflerent occasions varied 

 by as much as 4cr. What the conditions were in the longest of these three 

 experiments w411 be seen from the following table. It will be referred to 

 again later (p. 17). 



Exp. 37. Nov. 6, 1906. Room temp. 11° C. 



Induction current 

 to nerve. 



Length, in millimetres, of 



Time, in thousandths of a second (o-), 



Strength. 



5,000 

 10,000 

 10,000 

 r),000 

 3,000 

 10,000 

 10,000 

 10,000 

 10,000 



muscle nerve nerve 



ni,.^n*ir.n ^rom cH- | fpom Cu from Cv 



uireciion. ^j.^^^,^ ^f electrode electrode 



nerve to 7;. to muscle, to cord. 



interval 



taken by between 



impulse to arrivals of 



reach p direct and 



directly of reflex 



(measured), effects at ^j 



1 (measured). 



to be de- i 



fi^'fr^t , Probable 



for trans- 

 mission in I 

 nerve I 

 (assumed). ' 



18-5 



17-8 



18-4 



18-9 



20-2 



22 



20 



21 



22 



2-1 

 2-1 

 2-1 

 2-1 

 2-1 

 2-1 

 1-9 

 2-1 

 1-9 



delay in 

 cord. 



16-4 

 15-7 

 16-3 

 16-8 

 18-1 

 19-9 

 18-1 

 19-1 

 20-1 



The length of nerve traversed from the place of excitation, through the 

 plexus, to the cord and back, was in most of my preparations about 60 mm. 

 Only occasionally, when large animals were used, was it 70 or even 80 mm. 

 Many different observers have measured the rate of propagation of an 

 impulse along fresh frog's nerve and found it to be about 30 metres per 

 second. It is also known that there is no delay in the dorsal ganglia.^ To 

 ascertain the time which elapsed in the cord itself during each response we 

 must therefore deduct as a rule about 2o-, but occasionally as much as 2-6cr, 



little difference to the time to be deducted for transmission in nerve as compared with the 

 time taken in the central nervous system, that this method seemed to me to be exact 

 enough for the pre.sent purpose. The relative length of nerve traversed in different 

 responses of the same preparation has, however, been in so far taken into account that 

 usually more has been deducted for transmission when the current was ascending than 

 when it was descending (see also p. 14). The sense in which I have used the words 

 " ascending " and " descending " will be obvious. It is not strictly correct in reference to 

 the muscle when the sensory fibres are being considered, and not the motor only. 

 1 Moore and Reynolds, J. Physiol., xxiii., 1898, Suppl. 



