Ever since the first full statement of the membrane theory (Bernstein, 1912) it has been widely believed that the mechanism of nervous conduction depends upon certain important differences between the concentrations of electrolytes inside and outside the nerve fibre. Bernstein had no evidence on this point and he relied for his argument on what evidence was available from analyses of muscle. We now know much about the composition of the intracellular fluid of invertebrate nerves (e.g. Lewis, 1952) and one analysis has been made of the electrolyte distribution in frog nerves (Fenn, Cobb, Hegnauer & Marsh, 1934). No study of the distribution of electrolytes in mammalian nerves, however, is apparently available.Estimations of the total content of Na, K and Cl in various mammalian (1954): Na and K. The information to be derived from these values is unfortunately greatly limited by complete uncertainty about the relative proportions of intra-and extracellular fluid and the relative proportions of total intra-and extracellular Na, K, or Cl. The present paper is an analysis of the distribution of Na, K and Cl in cat nerves, based upon: (a) a comparison of the total Na, K and Cl contents of intact nerve trunks and desheathed nerve bundles; (b) studies of the diffusion of Na from desheathed nerve bundles; (c) a direct estimate of the intracellular space obtained from photomicrographs.
METHODSAnimals. Most of the nerves analysed were from cats. A small number of nerves from rabbits, dogs and monkeys were also studied for comparison; the only estimations made, however, were of the total Na and K.The majority of the nerves were removed from cats which were in good condition, with their circulation intact, in the course of experiments under general anaesthesia, or in some cases, after * Beit Memorial Research Fellow.