Monospecific, polyclonal antibodies to the nodC and nodA gene products of Rhizobium meliloti were used in combination with immunogold labeling and transmission electron microscopy to localize the NodC and NodA proteins in cultures of R. meliloti. Both NodC and NodA were detected in the cytoplasm and cell envelope in thin sections of free-living rhizobia treated with luteolin, a known inducer of nod gene expression; however, only NodC was detected on cell surfaces when immunolabeling was performed with intact induced cells. In view of biochemical data characterizing NodC as an outer membrane protein with a large extracellular domain, the pattern of immunolabeling on thin sections suggests that NodC is produced on free cytoplasmic ribosomes prior to assembly in the membrane. The pattern of NodA labeling on thin sections is consistent with biochemical data detecting NodA in both soluble and membrane fractions of NodA-overexpressing strains of R. meliloti.

The controversial metaplastic potential of the meninges1 has led to a number of varying accounts in medical literature about the relationship of neoplastic adipose tissue to the covering membranes of the central nervous system.Reports of a supposedly congenital lipoma in the left cerebral hemisphere, of an extradural lipoma that compressed the lumbar spinal cord, and of a similar sacral tumor represented the compass of FELDMAN'S5 information on such intracranial and intraspinal neoplasms in bovine animals. FELDMAN5 examined a lipoma from the brain of a slaughtered hog. JACKSON' cited a congenital lipoma in the meninges of a sheep. WILL IS^^ mentioned lipomas related to the central nervous system in conjunction with various malformations in man and referred to some of these neoplasms in animals designated by FELDMAN5. In their discourse on the classification of meningiomas, BAILEY and BUCY~ referred to the lipomatous type with cells typical of adipose tissue. These authors stated that Virchow was one of the first to maintain that lipomas arise from cells of the human meninges. BROWN'S~ rather elaborate study of 130 cases of intraspinal meningiomas in man resulted in a somewhat modified presentation of the variants as compared with that of BAILEY and BUCY~. In an apparently significant deviation from the trend at least partially established by the latter writers, BROWN^ emphasized that only those lipomas characterized by meningothelial (arachnoidal) cells as an integral part of the neoplastic tissue were classed as lipomatous meningiomas. Neoplasms comprised only of fat cells were not included with this category but were regarded as pure lipomas despite their meningeal locations. WILL IS^^ omitted the lipomatous form from an outline of the variants of meningiomas. In a slightly simplified version of the outline propounded by BROWN^, ANDERSON~ regarded the lipomatous form as a variant of the metaplastic meningioma. Among the brief presentations on meningiomas in certain veterinary textsee 8810, only INNES and SAUNDERS~ explicitly mentioned the lipomatous type.STOOKEY'S~~ report concerning the occurrence of extradural and intradural spinal lipomas in 19 people indicated pial derivation of the uncomplicated fatty neoplasms found beneath the dura mater. Apparently all of the intradural growths essentially contained well-differentiated adipose tissue, and intramedullary fibrous extensions from the pia mater often accompanied them. The account rendered by

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