Fixation in Cytochemistry and Electron-Microscopy

The purpose of the address is to point out the need for a fuller study of fixation for electron-microscopy, and especially to urge that cytochemists should interest themselves more actively in the interpretation of electron-micrographs. In some cases there is strong reason to suppose that the detailed structure seen in micrographs represents rather well the structure present in life. Certain globules in the neurones of the common snail, Helix aspersa, are carefully considered in this connection. In other cases, on the contrary, it is probable that the detailed structure seen in electron-micrographs does not represent the living condition. The structure is better interpreted as a reaction-product between the fixative used and what was present in life. In many cases, much of the detail is likely to be caused by the unmasking of hydrophil lipids from lipoprotein complexes. Such lipids, after unmasking, would be likely to arrange themselves in double membranes. The different ways in which fixatives may react with lipoproteins ate briefly described.