412 ANNALS NEW YORK ACADEMY OF SCIENCES 



axon and on the fin nerve of squid have shown that eserine alters, and, 

 in higher concentrations, abohshes, the nerve action potential. Within 

 a few minutes in eserine, amplitude, length, and duration of the action 

 potential recorded with the cathode ray oscillograph are markedly 

 changed, and in 20 to 25 minutes, the conductivity has been abolished 

 (figure 5) . When the nerves are put back into sea water, they 

 c^uickly recover, and conductivity reappears. The reversibility of the 

 effect is consistent with the fact that the inhibition of cholinesterase 

 is easily reversible in vitro. 



Strychnine, another inhibitor of cholinesterase, was also found to 

 alter, and, in higher concentrations, to abolish, the nerve action poten- 

 tial reversibly. 



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Figure 6. Effect of prostigmine on single fiber action potential (giant axon). Records before 

 and after 45' in O.OIM. 



Thus, a new relationship has been established between enzyme activ- 

 ity and nerve action potential, in this case using the peripheral axon. 



Prostigmine has, in vitro, the same effect as eserine, but it has no 

 effect on the nerve action potential (figures 6 and 7). Prostigmine 

 is like ACh, a quaternary ammonium salt, and it cannot penetrate the 

 lipoid membrane. This has been demonstrated by the following ex- 

 periment. The axoplasm of the nerves kept in eserine was extruded, 

 and the presence of the compound was tested by the inhibitory effect 

 on a purified cholinesterase solution. Even in thousand-fold dilution, 

 the axoplasm from a portion of a single axon showed, by the inhibition 



