NACHMANSOHN: CHEMICAL MECHANISM IN NERVES 417 



liberated 520 cmm. CO2, instead of 790 cmm. CO2 per hour without 

 DFP. The activity decreased slo"wly, over a period of hours. In 

 the solution exposed to the stronger concentration of DFP, the activity 

 was only 25 per cent and was nearly completely abolished after 30 

 minutes. If, after varying periods of exposure of the enzyme solution 

 to DFP in greater concentration, the solution was diluted, part of the 

 activity could be retained for a period of two to three hours (figure 

 10) . These experiments give additional evidence that the irreversible 

 inhibition of cholinesterase by DFP is a slow process at low tem- 

 perature. 



MINUTES 



Figure 10. Reversibility of cholinesterase inhibition bv DFP in vitro, tested by dilution 

 effect, t = 9° C. 



The cholinesterase solutidn used liberates 790 cmm. CO2 per hour. 

 + — + Activity found in presence of 0.1 /ig. of DFP per cc. 

 O — ^ O Activity found in presence of 0.5 fig. of DFP per cc. 

 • — • Activity found after exposure to 0.5 /ig. of DFP per cc, for varj'ing periods of time, 



and subsequent dilution to 0.1 ng. per cc. The part with the dotted lines indicates 



the reversibility as a function of time. 



Dr. Oilman presented observations on bullfrogs, in which it was 

 found that, following injection of DFP, the action potential of the 

 sciatic nerve may persist in the apparent absence of cholinesterase. 

 The bullfrog sciatic nerve contains extremely small amounts of cholin- 

 esterase. 100 mgs. of nerve (wet weight) liberate 40-50 cmm. CO2 

 per hour. Observations on lobster nerve indicate that the enzyme is 

 present in about five times excess, since about 80 per cent may be re- 

 moved while the action potential is unaffected. Even if, in the bull- 

 frog sciatic nerve, the excess of enzyme is smaller when part of the 



