PHYSIOLOGY: A. G. MAYER 
273 
The presence of these positively charged cations must tend to reduce 
the surface tension of the colloidal particles, and with it the negative 
potential. In fact the sudden augmentation of the negative charge 
upon any one of the colloidal particles would attract other positive ca- 
tions from the surfaces of neighboring particles and initiate a local nega- 
tive potential which would travel through the nerve. 
It is more probable however that, as the velocity of nerve conduction 
is proportional to the degree of concentration of the adsorbed sodium, 
calcium, and potassium cations, these cations themselves initiate the 
reaction and form some reversible chemical compound with some pro- 
teid substance, thus temporarily neutralizing their positive charges and 
unmasking the negative charges upon the colloidal particles to the sur- 
faces of which they were attracted by adsorption. 
These various hypotheses are suggested not so much as possible ex- 
planations of the phenomenon of nerve conduction, but more to stimu- 
late interest in the problem and to suggest directions for further research. 
It is perhaps a step in advance to know that, whatever its precise nature, 
nerve conduction is some chemical reaction involving the adsorbed so- 
dium, calcium, and potassium cations, and thus its rate is proportional 
to the concentration of these adsorbed ions. 
The almost instantaneous recovery observed when the medusa is 
taken out of dilute sea water or magnesium solutions and replaced in 
natural sea water, and the very short time required to assume a con- 
stant rate of nerve conduction when the medusa is placed in concen- 
trated or diluted sea water is readily explained by the theory that nerve 
conduction is dependent upon the adsorption of the conducting cations 
by negatively charged colloidal particles and is thus a surface effect. 
The previous work of Meltzer and Auer, Mines, and Mayer has 
shown that it is probable that the calcium enters into combination with 
the sodium, possibly forming an ion-proteid. It now seems probable 
that this intimate association between calcium and sodium takes place 
upon the surfaces of the particles of the colloidal nerve fluid or some 
other colloidal elements of the nerve. 
In this brief summary it may be inexpedient to review the literature 
of the subject, but the bearing of this research upon the observations 
of Macallum, 1913, upon changes in surface tension in active cell mem- 
branes, and of Tashiro, 1914, upon the production of carbon dioxide by 
active nerves (see these Proceedings, 1, 110), is apparent, and the con- 
tention of R. S. Lillie that cell surfaces play the important role in stimu- 
lation is strongly supported. 
