THREE FIGURES
Feng and Gerard ('30) demonstrated a striking difference in the behavior of nerve depending upon whether its connective tissue sheath was intact o r split. The nerve with split sheath after asphyxiation could be made to recover by mere washing with 0,-free Ringer while the intact nerve could not. In nerve with split sheath, the rate of block due to various solutions such as isotonic glucose, CaC1, and KC1 was many times greater than in intact nerve. From such experiments they naturally concluded that the connective tissue sheath was an effective diffusion barrier. Recently Lorente de N6 ( '47, pp. 23-24), hovever, impressed by the rapidity with T V E C ~ KCI solution produces conduction block in nerve o r NaCl solution restores conduction to nerve previously dcprived of sodium ions, has thought it justifiable to make such strong comments on the previous conclusion of Feng and Gerard ( '30) as the following: "It is utterly impossible to believe that the connective tissue sheath of frog or bull-frog nerve could act as a diffusion barrier that would delay for considerable periods of time the penetration of solutes into the nerve. )' A reexamination of this question thus becomes worthtvhile. Our attention was forcibly drawn to the need for this reexamination in the course of research devoted to the analysis of the depolarization curves in nerve produced by various agents, especially potassium.