In constructing a model for demonstration of the function of the cochlea two assumptions are what we ought to keep clearlyoutof our mind: (1) that the living cochlea might containdeadbuilding material of such physical properties as vulcanized rubber or tensile metal, (2) that the cochlea might containcontractiletissue, muscle tissue, that is, building material, which, in itself or in the supports in which it is inserted, could, from time to time at least, actively produce any stresses.A mechanical theory must recognize four salient features: (1) that any sound pervades the cochlea no matter whether the window flexibility is considered in theorizing or put down as negligible in theorizing or is actually (pathologically) impaired—just as any sound pervades any building with all its rooms and partititions, and that such aprimitive functionis almost certain to have at least a weak and otherwise limited stimulating effect; (2) that the main andmore adequate(but not exclusive) stimulating effect in mammalian animals (having an elongated cochlea tube) is likely to result from displacements of the phragma due to pressure differences between the windows, which are unsymmetrical to the meatus; (3) that thebulgeformed by the displaced phragmacan not travel, but can only lengthen itself, as is demonstrated by inspection of the hydraulic model; (4) that the formation of a bulge on either side of the average location of the phragma issucceededby the development ofstressin the phragma, as is demonstrated by inspection of the hydraulic model.