DAVID NACHMANSOHN 



choline which may be split in these organs may amount to several 

 kilograms per hour or several milligrams in one-thousandth of a second. 

 The concentration is of the same order of magnitude as was calculated 

 for the motor end plate by Marnay and Nachmansohn (10). It is 

 suiliciently high to make possible the assumption that acetylcholine 

 is directly connected with the discharge, which requires that the com- 

 pound must appear and disappear in milliseconds. If speculation 

 were to be excluded, the only means of removing this compound so 

 rapidly is enzymic action. The high concentration of a specific en- 

 zyme appeared particularly significant in view of the chemical con- 

 stitution of these organs. They contain 92% water and only 2% pro- 

 tein. The discharge is, in these organs, the main function; there is 

 no question here of a transmission of the nervous impulse to a second 

 unit, since there is none. 



In the weak electric organ of the common ray, the concentration 

 of choline esterase is relatively low. If in the three species mentioned, 

 voltage and number of plates per centimeter are compared with the 

 concentration of choline esterase, a close relationship becomes obvious. 



A more detailed analysis has been carried out of the electric 

 organ of E. electricus. This species is particularly favorable for such 

 studies because the number of plates per centimeter, and conse- 

 quently the voltage per centimeter, decreases from the head to the 

 caudal end of the organ. The choline esterase activity decreases in 

 the same proportion. If the electric changes are recorded and com- 

 pared with the chemical values at the same section, a close parallelism 

 is obtained between voltage and enzyme concentration. This is found 

 not only in regard to the variations which occur in the same specimen, 

 but even in absolute amounts for the variations between the individuals 

 (12). In measurements covering a range from 0.5-22 v. per cm., 

 the line correlating the physical and chemical event was found to in- 

 dicate a direct proportionality. 



The voltage developed in the discharge depends upon the elec- 

 tromotive force and the resistance. Two assumptions therefore appear 

 possible regarding the way in which acetylcholine may act. It may 

 produce an electromotive force directly by action on the surface, or 

 it may decrease the resistance by increasing the permeability of the 

 boundary. Resistance and electromotive force are closely related 

 properties. The drop in resistance during the passage of the impulse, 



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