The complex fat of the myelin becomes altered chemically, while the other components of the sheath break down.

In secondary encephalitis, symptoms usually begin five to ten days after the onset of the disease itself and are related to the breakdown of the myelin sheath that covers nerve fibers.

A little later the breaking down of the whole axon, both axis cylinder and myelin sheath alike, seems to occur simultaneously throughout its entire length distal to the place of severance.

Some other glycerides isolated from natural sources are analogous in composition to tristearin, but with this difference, that the three radicals which replace hydrogen in glycerin are not all identical; thus kephalin, myelin and lecithin are glycerides in which two hydrogens are replaced by fatty acid radicals, and the third by a complex phosphoric acid derivative.

The Schwann cell has an extensive cytoplasm which allows it to wrap a myelin sheath around nerve axons.