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Although the number of applications of conductive staining for SEM has recently increased investigations or discussions on the features of these methods are scanty, and so it could not be said that its features are sufficiently understood. In the present studies employing the tannin‐osmium method as the conductive stain, the authors compared it with an ion‐sputtering method that they use for metal coating. Besides the prevention of masking by the coating metal, there are other advantages to the conductive staining method. The appearance of the tissue “transparency”, which allows three‐dimensional observations of sub‐surface structures to be made. Any damage associated with metal coating can be avoided since the specimen itself is conductive. Hardening of specimens by the conductive stain enhances the resistance of structures to mechanical damage during preparation. Especially the tissue transparency produced by the conductive stain might suggest new possibilities for SEM.

We studied sialic acid in the cerebrospinal fluid (CSF) of 52 children with leukemia and 51 children with non-leukemic diseases. The CSF sialic acid concentration in the children with central nervous system (CNS) leukemia was significantly higher than that in the children with acute lymphoblastic leukemia without CNS involvement, acute non-lymphocytic leukemia without CNS involvement, non-hemopoietic diseases, non-suppurative meningitis, epilepsy, and other neurologic diseases. Serial determinations revealed a rapid decline in the CSF sialic acid concentrations in the patients with CNS leukemia who responded well to the therapy and who were free from relapse of CNS leukemia. The simultaneously determined CSF beta 2 microglobulin concentration did not show any significant changes. These results suggest that the CSF sialic acid may be a good indicator of CNS leukemia.