Quarterly Journal of Microscopical Science, Vol s3-96, 337-341, Copyright © 1955 by Company of Biologists

Studies of the Impregnation of Nervous Tissue Elements

II. The Nature of the Compounds Responsible for the Impregnation of Axons; Practical Considerations

¹ Department of Pathology, The Hebrew University, Hadassah Medical School, Jerusalem, Israel

Axoplasm and axolemma differ in their chemical and physical characteristics. The impregnation of axons is mainly due to a compound which is soluble in hot organic solvents and which appears to be situated in the axoplasm.

Ethylenic linkages and hydroxyl groups play no role in the impregnation of axons. Sulphydryl and carbonyl groups appear to be partly responsible. These groups are situated mainly in the axoplasm, although sulphydryls are present also in the axolemma. The impregnation of axolemma depends to a great extent on chemical groups which could not be identified.

The fact that solutions of Ag diammine are more suitable for impregnating axons than those of AgNO₃ might be due to one of the following factors: (i) that the reducing groups of the axons are more easily oxidized at high pH levels; (2) that the complex diammine ion might exert a higher oxidizing activity when reacting with some tissue molecules; (3) that the rate of reaction of the reducing groups of the tissue with the Ag diammine ion might be faster than that with the silver ion.

The Bielschowsky procedure may be carried out successfully on sections of tissue embedded either in paraffin wax or carbowax. With the former procedure care should be taken to minimize contact with mixtures of hot solvents. A further intensification of impregnation of paraffin sections is obtained by treating sections for 24 hours in 4% formaldehyde prior to the Bielschowsky procedure.