390 ANNALS NEW YORK ACADEMY OF SCIENCES 



brane would be the site of a complex chemistry. Although the dis- 

 cussion of the chemical side of nerve activity is beyond the scope of 

 this paper, I should hke to conclude by turning to some interesting 

 observations of von Muralt (1942), involving the appearance, during 

 excitation, of a substance which may bring about the reversal of the 

 membrane polarization. 



When an excised frog sciatic is stimulated, electrically, at a certain 

 frequency and simultaneously is dipped with a certain velocity into 

 liquid air, several excitation waves must be caught and frozen along 

 the nerve. When an extract of stimulated and unstimulated nerves, 

 pulverized in the frozen state, is made up with eserinized frog Ringer 

 or serum, it appears that, during excitation, the nerve has liberated 

 minute amounts of several substances. One of these, by various tests, 

 is identified as acetylcholine ; and a second substance is concentrated in 

 the foam of the extract, which, from this sign of surface activity, 

 possibly indicates the presence of a nonpolar-polar substance, whereas, 

 in the foam from an acetylcholine-eserin-serum solution as a control, 

 the acetylcholine fails to show an accumulation. Recently, by the 

 same freezing method, von Muralt has intercepted a third substance, 

 thiamin, which possibl)^ also is surface-inactive.-^ Certainly, these 

 results are far from giving conclusive support to the concept that non- 

 polar-polar substances, detectable by their surface activity, have been 

 liberated during excitation. Even if they were, the liberation may be of 

 minor significance, considering the fact that, according to Hopkins and 

 Huxley, and to Curtis and Cole, the resting potentials of the giant 

 nerve fibers vary little from one experiment to another, in contrast to 

 a wide variability appearing in the size of their action potentials. In 

 any case, this grouj) of observations emphasizes the urgent need to 

 extend the study of chemical products, which are directly connected 

 with nerve activity, beyond the demonstration of acetylcholine. 



BIBLIOGRAPHY 



1. Hbber, R. 



1905. Pfliig. Arch. ges. Physiol. 106: .599. 



2. Hodgkin, A. L., & A. F. Huxley 



1939. Nature 144: 710. 

 1945. J. Physiol. 104: 176. 



Webb, D. A.", & J. Z. Young 



1940. .1. Physiol. 98: 299. 



3. Curtis, H. J., & K. S. Cole 



1942. .1. Cell. Comp. Physiol. 19: 135. 



4. Osterhout, W. V., et al. 



1927. J. Gen. Physiol. 11: 193. 



