1910.] The Effect of some Local Anesthetics on Nerve. 423 
During these periods the muscle twitches were recorded on a drum moving 
about 1 cm. per minute, whilst a double electro-magnetic signal (Locke’s 
model), writing below the muscle tracing, served to record time and stimuli. 
The inductorium was either (A) a Cambridge model which, with signal in 
primary circuit and a current of 0°6 ampere from a single accumulator, was 
used with the secondary coil at 175 mm.,‘or (B) a model of Berne type 
which, under the above conditions, carried 0°-4 ampere and was used with the 
secondary 400 mm. from its zero. In both cases the stimulus was well in 
excess of that necessary to evoke maximal response from a good nerve- 
muscle, and any preparation that failed to respond maximally was rejected. 
III. ConDITIONS WHICH INFLUENCE THE ANASTHETIC BLOCK. 
It was to be expected that the rate of diffusion of the drugs into the 
nerve would influence the rate of onset of the block. This was substan- 
tiated by our preliminary tests, in which we found that an N/100 solution of 
cocaine hydrochloride required 40 minutes to produce on the sciatic- 
gastrocnemius an effect attained, with the same solution, on the nerve- 
sartorius, in about one-twentieth of the time. So great a difference shows 
that, even with the same nerve from different frogs, variations in the rate 
of blocking may be expected from minor variations in the position of the 
motor fibres relatively to the surface exposed to the drug. 
Individual nerves differ in quality; eg. a fresh preparation from a fresh 
frog is blocked more rapidly than a preparation either stale or made from a 
frog that has been kept in stock for some time. As would be anticipated, 
increase in concentration of the drug solution, or repetition of the drug bath 
soon after recovery from a block, leads to more rapid abolition of conductivity. 
With dilute solutions of the drugs, decrease in temperature, when suffi- 
ciently great, delays the onset of the block, especially in the case of cocaine, 
but between 16° and 20° C. the effect of temperature is often masked by 
other factors. 
For a given position of the secondary coil, a block which is complete to 
maximal break shocks is almost invariably complete to tetanic stimulation. 
When not so, the response to the latter is seldom tetanus, but the: brief 
clonus or apparently simple twitch noticed by Wedenski, and later by Tait 
and Gunn (in the case of yohimbine), and is rarely obtainable more than 
once. | 
Moreover, when a block is once complete, the stimulus may be consider- 
ably increased without provoking further response. With inductorium A, a 
block with the secondary coil at 175 mm. was invariably a block when the 
secondary was pushed up to zero, both for single shocks and for tetanic 
