Quarterly Journal of Microscopical Science, Vol s3-89, 89-102, Copyright © 1948 by Company of Biologists

Observations on the Chemical Composition of Myelin and the Smallest Size of Myelinated Nerve-Fibres in the Central Nervous System

¹ Department of Human Anatomy, Oxford

Baker's (1946) acid haematein and pyridine-extraction control tests, claimed to be specific for phospholipines (Baker, 1947), have been applied to various parts of the central nervous system of rats and man. The sudan black method for the detection of lipoids and the nile blue method for the staining of acidic lipoids have also been used.

The findings are in agreement with older statements in the literature that myelin contains a considerable amount of phospholipines. It was impossible to determine whether galactolipines or neutral lipoids are also present.

In the acid haematein-stained sections finer fibres were seen than when other stains for myelin sheaths are employed. Fibres with a diameter of 0.5 µ or even somewhat less were stained in various parts of the central nervous system of rats. It is regarded as probable from these findings that fibres down to 0.5 µ or even smaller possess a lipoid investment. These observations lend support to the now commonly accepted view that the distinction between myelinated and so-called unmyelinated fibres is arbitrary. Some observations are made, however, which indicate that the presence of truly unmyelinated fibres cannot be excluded.