Qualitative studies on nerve birefringence have in the past indicated many important facts regarding the ultrastructure of the individual axons. In order to apply the sensitive optical method in greater detail to such investigations quantitative methods are necessary. It is also desirable that such procedures be applicable to the axons under physiological conditions. The myelin sheaths of the nerve fibers are most readily studied optically in this way because of their high birefringence, but the chief difficulties in the interpretation of the observations result from the radial orientation of the optic axes of the sheath elements. In this paper are presented simple mathematical considerations leading to an expression relating the experimentally measured sheath retardation and axon and sheath dimensions to the birefringence of the sheath, calculated as an intrinsic property of the sheath elements. Consideration of possible theoretical errors leads to confidence that the results obtained are accurate within a few percent. Typical frog sciatic axons show a birefringence of about 0.011, which is a fairly large value for biological materials. The results supplement x-ray evidence for a high degree of molecular or micellar orientation in the myelin sheath.
© 1936 Optical Society of AmericaFull Article | PDF Article
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