The occurrence and significance of myelin with unusually large periodicity.

The occurrence of myelin with an unusually large periodicity has been noted in a variety of human and animal diseases by many authors. It has also proved possible to create regular alterations in periodicity by various treatments of fresh unfixed nerve. We have quantified the changes found in material from a variety of sources and conclude that they are compatible with the occurrence of physicochemical changes in the myelin membranes, leading to overhydration.