NACHMANSOHN: CHEMICAL MECHANISM IN NERVES 399 



nomena occur at the surface. The high concentration of the enzyme 

 at the surface suggested that ACh may be connected with conduction 

 along the axon, as well as with transmission across the synapse. This 

 view is consistent with the conclusion of neurophysiologists that the 

 mechanism of these two events is fundamentally the same. 



II. CORRELATION BETWEEN ENZYME ACTIVITY AND 

 PHYSICAL EVENTS DURING NERVOUS FUNCTION 



The high rate of ACh metabolism and the locahzation of the enzyme 

 at the neuronal surface made possible the assumption that the ester is 

 connected with the electrical manifestations of nerve activity. How- 

 ever, suggestive as these facts may be, observations on enzymes, as 

 pointed out before, do not permit an interpretation of the actual role 

 of the substrate. For an understanding of the precise function of an 

 enzyme, its activity has to be connected with events in the living cell 

 which, in the case of nerve, can only be recorded by physical means. 

 Such a relationship has been established in three different ways. 



A. Parallelism Between the Voltage of the Action Potential and 



Cholinesterase Activity 



The first line of investigations in which a correlation between physi- 

 cal and chemical processes was obtained, was in experiments on the 

 electric fish. It was found that the activity of cholinesterase in the 

 electric organ parallels exactly the voltage of the action potential. 



The powerful electric discharge in these organs is identical in nature 

 with the nerve action potential of ordinary nerves (A. V. HilP*). The 

 only distinction is the arrangement of the nervous elements, the elec- 

 tric plates in series. The potential difference developed by a single 

 element is about 0.1 volt, which is the same order of magnitude as that 

 found in ordinary nerves. In the species with the most powerful elec- 

 tric organ known, Electrophonis electricus, the so-called electric eel, 

 several thousand elements are arranged in series from the head to the 

 caudal end of the organ. Thus, the voltage of a discharge amounts 

 to 400-600 volts, on the average, and, in some specimens, more than 

 800 volts have been observed. In Torpedo, another species with a 

 powerful electric organ, the elements are arranged in a dorso-ventral 

 direction. Since it is a flat fish, the number of plates in series usually 

 does not exceed 400 to 500, and, consequently, the discharge is only 30 

 to 60 volts, on the average. 



In 1937, an extraordinarily high concentration of cholinesterase was 

 found in the strong electric organ of Torpedo. In the following year, 



