FROM analysis by means of polarized light it has long been known that nerves possess a high degree of molecular organization. The axis cylinder is positively birefringent due to the presence of anisotropic material, the optic axis of which lies parallel to the long axis of the fiber. The myelin sheath is constructed of lipoid fluid crystals with optic axes perpendicular to the direction of the fiber and radially oriented (Schmidt, 18). The positive birefringence of the axis cylinder is due presumably to the protein neurofibrils which, though visible in fixed and stained preparations, have never been demonstrated in living medullated axons under physiological conditions (Peterfi, 16). In view of the success with which the x-ray diffraction method for fine-structure analysis has been applied to certain other fibrous animal tissues such as hair, chitin, connective tissue, etc., it is desirable that full use be made of this tool in the case of nerve, particularly since modern research on nerve energetics reve...