Formaldehyde is still the ideal fixation medium for the preservation of brain tissue. It hardens such material in bulk rapidly and uniformly; it is of great service in the study of changes in the central nervous system, for it offers an opportunity to retain the specimen in its uncut and undisturbed shape for gross morphologic studies before it is dismembered for finer cytologic observations. There is, however, one difficulty—and that is, because of the great assortment of methods devised for a better display of the various components of the nerve tissue and their numerous pathologic changes, there is need of a large variety of fixatives. This holds true for the many methods of staining neuroglia, and it is particularly essential for Cajal's1gold chloride and sublimate method as well as for its more recent modifications introduced by Achucarro and Del Rio Hortega.2 Cajal's staining method demands that fresh