1910.]| The Effect of some Local Anesthetics on Nerve. 429 
trunk is slow (v. supra, p. £25). Hence the more superficial fibres of the nerve 
must be affected distinctly earlier than the deeper ones. This raises the question 
whether incomplete blockage of a nerve trunk is due to partial blockage of any 
of its individual fibres, or to complete blockage of a limited number of them. 
In all our records, the muscular response, and therefore also the 
conductivity of the nerve, fails abruptly when it fails at all; either abruptly 
and rapidly as in fig. 1, or abruptly and slowly by a limited number of sharply 
defined, flat-topped steps, not exceeding eight in total. Marked instances of 
the latter are seen in figs. 2 and 3, as the effect of solutions that lead slowly 
to complete blockage of the nerve trunk. 
Fig. 3.—Block by a slowly acting Anesthetic Solution. The drug, cocaine hydrochloride 
N/500 (= 0:07 per cent.), was applied at the white vertical line. 
These do not represent the block in individual nerve fibres to be anywhere 
partial, but, as judged by the muscle, to be either complete or zero. 
For, on the one hand, the large number of small decrements in response 
‘that such partial blocking would necessarily entail is conspicuously absent, 
and, on the other hand, the strikingly small number and extreme flatness 
of the steps suffice to indicate that each one represents simultaneous 
complete blockage of large groups of fibres. The blockage of individual 
fibres is therefore commenced and completed within the interval (10 seconds)* 
between the stimuli. 
Nor is partial blockage of individual fibres in evidence when the drug fails 
to produce completet blockage of the nerve trunk. 
* A small number of observations with stimulation at intervals of 5 seconds yielded, 
without exception, records of the same type. 
+ A block was not regarded as complete until at least three consecutive stimuli 
evoked no response. 
VOL. LXXXIII.—-B. 2K 
